diff --git a/go.mod b/go.mod
index 4d37f4d3..435d3ecb 100644
--- a/go.mod
+++ b/go.mod
@@ -15,7 +15,7 @@ require (
 	golang.org/x/crypto v0.0.0-20191002192127-34f69633bfdc // indirect
 	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
 	gopkg.in/yaml.v2 v2.2.2
-	mvdan.cc/sh/v3 v3.1.0
+	mvdan.cc/sh/v3 v3.1.1
 )
 
 go 1.13
diff --git a/go.sum b/go.sum
index 31d208e7..13af05a9 100644
--- a/go.sum
+++ b/go.sum
@@ -65,5 +65,5 @@ gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 mvdan.cc/editorconfig v0.1.1-0.20200121172147-e40951bde157/go.mod h1:Ge4atmRUYqueGppvJ7JNrtqpqokoJEFxYbP0Z+WeKS8=
-mvdan.cc/sh/v3 v3.1.0 h1:bFxsEzIubuABloc8G1Ko78rbZZ0JspNN9e9+R/w3z5k=
-mvdan.cc/sh/v3 v3.1.0/go.mod h1:F+Vm4ZxPJxDKExMLhvjuI50oPnedVXpfjNSrusiTOno=
+mvdan.cc/sh/v3 v3.1.1 h1:niuYC5Ug0KzLuN6CNX3ru37v4MkVD5Wm9T4Mk2eJr9A=
+mvdan.cc/sh/v3 v3.1.1/go.mod h1:F+Vm4ZxPJxDKExMLhvjuI50oPnedVXpfjNSrusiTOno=
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 47f1bb96..6a5fb8ac 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -39,7 +39,7 @@ golang.org/x/xerrors
 golang.org/x/xerrors/internal
 # gopkg.in/yaml.v2 v2.2.2
 gopkg.in/yaml.v2
-# mvdan.cc/sh/v3 v3.1.0
+# mvdan.cc/sh/v3 v3.1.1
 mvdan.cc/sh/v3/expand
 mvdan.cc/sh/v3/interp
 mvdan.cc/sh/v3/pattern
diff --git a/vendor/mvdan.cc/sh/v3/interp/vars.go b/vendor/mvdan.cc/sh/v3/interp/vars.go
index 8a6fe35f..3529e190 100644
--- a/vendor/mvdan.cc/sh/v3/interp/vars.go
+++ b/vendor/mvdan.cc/sh/v3/interp/vars.go
@@ -41,6 +41,18 @@ func (o overlayEnviron) Each(f func(name string, vr expand.Variable) bool) {
 func execEnv(env expand.Environ) []string {
 	list := make([]string, 0, 64)
 	env.Each(func(name string, vr expand.Variable) bool {
+		if !vr.IsSet() {
+			// If a variable is set globally but unset in the
+			// runner, we need to ensure it's not part of the final
+			// list. Seems like zeroing the element is enough.
+			// This is a linear search, but this scenario should be
+			// rare, and the number of variables shouldn't be large.
+			for i, kv := range list {
+				if strings.HasPrefix(kv, name+"=") {
+					list[i] = ""
+				}
+			}
+		}
 		if vr.Exported {
 			list = append(list, name+"="+vr.String())
 		}
diff --git a/vendor/mvdan.cc/sh/v3/syntax/lexer.go b/vendor/mvdan.cc/sh/v3/syntax/lexer.go
index 9510d1ff..f80da0dc 100644
--- a/vendor/mvdan.cc/sh/v3/syntax/lexer.go
+++ b/vendor/mvdan.cc/sh/v3/syntax/lexer.go
@@ -993,7 +993,7 @@ func (p *Parser) advanceLitRe(r rune) {
 				p.quote = noState
 				return
 			}
-		case ' ', '\t', '\r', '\n':
+		case ' ', '\t', '\r', '\n', ';', '&', '>', '<':
 			if p.rxOpenParens <= 0 {
 				p.tok, p.val = _LitWord, p.endLit()
 				p.quote = noState
@@ -1002,7 +1002,7 @@ func (p *Parser) advanceLitRe(r rune) {
 		case '"', '\'', '$', '`':
 			p.tok, p.val = _Lit, p.endLit()
 			return
-		case utf8.RuneSelf, ';', '&', '>', '<':
+		case utf8.RuneSelf:
 			p.tok, p.val = _LitWord, p.endLit()
 			p.quote = noState
 			return
diff --git a/vendor/mvdan.cc/sh/v3/syntax/parser.go b/vendor/mvdan.cc/sh/v3/syntax/parser.go
index d3fe6c3c..16ccd242 100644
--- a/vendor/mvdan.cc/sh/v3/syntax/parser.go
+++ b/vendor/mvdan.cc/sh/v3/syntax/parser.go
@@ -545,12 +545,26 @@ func (p *Parser) doHeredocs() {
 		if i > 0 && p.r == '\n' {
 			p.rune()
 		}
+		lastLine := p.npos.line
 		if quoted {
 			r.Hdoc = p.quotedHdocWord()
 		} else {
 			p.next()
 			r.Hdoc = p.getWord()
 		}
+		if r.Hdoc != nil {
+			lastLine = r.Hdoc.End().line
+		}
+		if lastLine < p.npos.line {
+			// TODO: It seems like this triggers more often than it
+			// should. Look into it.
+			l := p.lit(p.npos, "")
+			if r.Hdoc == nil {
+				r.Hdoc = p.word(p.wps(l))
+			} else {
+				r.Hdoc.Parts = append(r.Hdoc.Parts, l)
+			}
+		}
 		if stop := p.hdocStops[len(p.hdocStops)-1]; stop != nil {
 			p.posErr(r.Pos(), "unclosed here-document '%s'", stop)
 		}
diff --git a/vendor/mvdan.cc/sh/v3/syntax/printer.go b/vendor/mvdan.cc/sh/v3/syntax/printer.go
index 53cce972..63f04402 100644
--- a/vendor/mvdan.cc/sh/v3/syntax/printer.go
+++ b/vendor/mvdan.cc/sh/v3/syntax/printer.go
@@ -165,26 +165,26 @@ type colCounter struct {
 	lineStart bool
 }
 
-func (c *colCounter) WriteByte(b byte) error {
+func (c *colCounter) addByte(b byte) {
 	switch b {
 	case '\n':
 		c.column = 0
 		c.lineStart = true
-	case '\t', ' ':
+	case '\t', ' ', tabwriter.Escape:
 	default:
 		c.lineStart = false
 	}
 	c.column++
+}
+
+func (c *colCounter) WriteByte(b byte) error {
+	c.addByte(b)
 	return c.Writer.WriteByte(b)
 }
 
 func (c *colCounter) WriteString(s string) (int, error) {
-	c.lineStart = false
-	for _, r := range s {
-		if r == '\n' {
-			c.column = 0
-		}
-		c.column++
+	for _, b := range []byte(s) {
+		c.addByte(b)
 	}
 	return c.Writer.WriteString(s)
 }
@@ -269,15 +269,15 @@ func (p *Printer) space() {
 }
 
 func (p *Printer) spacePad(pos Pos) {
-	if p.wantSpace {
-		p.WriteByte(' ')
-		p.wantSpace = false
-	}
 	if p.cols.lineStart {
 		// Never add padding at the start of a line, since this may
 		// result in broken indentation or mixing of spaces and tabs.
 		return
 	}
+	if p.wantSpace {
+		p.WriteByte(' ')
+		p.wantSpace = false
+	}
 	for !p.cols.lineStart && p.cols.column > 0 && p.cols.column < int(pos.col) {
 		p.WriteByte(' ')
 	}
@@ -331,7 +331,7 @@ func (p *Printer) writeLit(s string) {
 		p.WriteString(s)
 		return
 	}
-	p.WriteByte('\xff')
+	p.WriteByte(tabwriter.Escape)
 	for i := 0; i < len(s); i++ {
 		b := s[i]
 		if b != '\t' {
@@ -340,7 +340,7 @@ func (p *Printer) writeLit(s string) {
 		}
 		p.WriteByte(b)
 	}
-	p.WriteByte('\xff')
+	p.WriteByte(tabwriter.Escape)
 }
 
 func (p *Printer) incLevel() {
@@ -370,11 +370,11 @@ func (p *Printer) indent() {
 	switch {
 	case p.level == 0:
 	case p.indentSpaces == 0:
-		p.WriteByte('\xff')
+		p.WriteByte(tabwriter.Escape)
 		for i := uint(0); i < p.level; i++ {
 			p.WriteByte('\t')
 		}
-		p.WriteByte('\xff')
+		p.WriteByte(tabwriter.Escape)
 	default:
 		p.spaces(p.indentSpaces * p.level)
 	}