cmd/go-contrib-init: fix in-GOPATH check

It's okay to have GOROOT=$HOME/go, GOPATH=$HOME.

That's what I have.

It's just not okay to hack in Go under $GOPATH/src.

Change-Id: I6ae69aceb43970bbdc9631ab090689a153954087
Reviewed-on: https://go-review.googlesource.com/45651
Reviewed-by: Steve Francia <spf@golang.org>

cmd/go-contrib-init/contrib.go

@@ -171,7 +171,7 @@ func inGoPath() bool {
 	}
 
 	for _, path := range filepath.SplitList(os.Getenv("GOPATH")) {
-		if strings.HasPrefix(wd, path) {
+		if strings.HasPrefix(wd, filepath.Join(path, "src")) {
 			return true
 		}
 	}