_js: bump to v0.4.0

Versions 0.3.2 and 0.3.3 were published in the master branch, to follow
the latest 2.6.x changes in the mvdan.cc/sh module itself.

The master.v3 branch has had quite a bit of work done that isn't in the
old v2 versions, so let's start updating NPM from this branch.

A few tweaks were necessary to get the module-aware gopherjs building
properly. Otherwise, everything works like it used to in the master
branch.

_js/build

@@ -1,5 +1,14 @@
 #!/bin/sh
 
+# If you get weird errors like 'undeclared name: CacheLinePadSize', try being
+# explicit about the Go 1.11.x GOROOT, like:
+#
+#     GOROOT=/usr/lib/go ./build
+
+export GO111MODULE=on # build in module-aware mode
+
 gopherjs build -o index.js || exit 1
 
 node testmain.js || exit 1
+
+go mod tidy # to remove unnecessary gopherjs lines from go.mod

_js/package.json

@@ -1,6 +1,6 @@
 {
 	"name": "mvdan-sh",
-	"version": "0.3.1",
+	"version": "0.4.0",
 	"description": "A shell parser and formatter (POSIX/Bash/mksh)",
 	"main": "index.js",
 	"repository": "https://github.com/mvdan/sh",

go.mod

@@ -8,3 +8,5 @@ require (
 	golang.org/x/sync v0.0.0-20181108010431-42b317875d0f
 	golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8 // indirect
 )
+
+replace github.com/gopherjs/gopherjs => github.com/myitcv/gopherjs v0.0.0-20181206184521-f5b96be2a04c