.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.