remove support for go 1.11 (#444)

.travis.yml

@@ -1,9 +1,9 @@
 language: go
 
 go:
-  - "1.11.x"
   - "1.12.x"
   - "1.13.x"
+  - "1.14.x"
   - tip
 
 install:

cmd/tlsconfig/tls_version_go11.go

@@ -1,31 +0,0 @@
-// +build !go1.12
-
-// This file can be removed once go1.11 is no longer supported
-
-package main
-
-import (
-	"crypto/tls"
-	"sort"
-)
-
-func mapTLSVersions(tlsVersions []string) []int {
-	var versions []int
-	for _, tlsVersion := range tlsVersions {
-		switch tlsVersion {
-		case "TLSv1.2":
-			versions = append(versions, tls.VersionTLS12)
-		case "TLSv1.1":
-			versions = append(versions, tls.VersionTLS11)
-		case "TLSv1":
-			versions = append(versions, tls.VersionTLS10)
-		case "SSLv3":
-			// unsupported from go1.14
-			versions = append(versions, tls.VersionSSL30)
-		default:
-			continue
-		}
-	}
-	sort.Ints(versions)
-	return versions
-}