.travis.yml: use 1.4, not release

from irc:

<jbenet> Any idea why this job isn't finding Go?
  https://travis-ci.org/jbenet/go-ipfs/jobs/49296465 --
  we havent had problems for a while and now lots of
  builds fail like this.
<•meatballhat> jbenet: still around?
<•meatballhat> jbenet: the `release` name was something specific to
  gvm. As there is no `release` tag in the go repo, it's no longer a
  valid target. What you probably want is `1.4.1` or `master`.
<jbenet> meatballhat: ah thank you
<•meatballhat> jbenet: np, sorry about the switchup!  gvm had been
  woefully undermaintained since August, so we were long overdue in
  replacing it.

.travis.yml

@@ -2,7 +2,7 @@ language: go
 
 go:
   - 1.3
-  - release
+  - 1.4
   - tip
 
 script: