cmd/go-contrib-init: fix get GOPATH env logic

Go runtime now uses user homedir+go (i.e. $HOME/go) if GOPATH
environment variable is not set.

Change-Id: I26d90e07976a5311ea19de8a6e2c63830b802882
Reviewed-on: https://go-review.googlesource.com/46234
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed