Ensure the $HOME env is being set on Windows

internal/homefix/homefix.go

@@ -0,0 +1,5 @@
+// Package homefix exists to address a bug where mvdan.cc/sh expects
+// $HOME to be available in order to be able to expand "~".
+//
+// This should delete this package once this is fixed there.
+package homefix

internal/homefix/homefix_windows.go

@@ -0,0 +1,15 @@
+package homefix
+
+import (
+	"os"
+
+	"github.com/mitchellh/go-homedir"
+)
+
+func init() {
+	if os.Getenv("HOME") == "" {
+		if home, err := homedir.Dir(); err == nil {
+			os.Setenv("HOME", home)
+		}
+	}
+}