[RFC] Remove Clang 3.4 installation in travis.sh.

Travis provides Clang 3.4 out of the box (see http://docs.travis-ci.com/user/languages/c/#CI-environment-for-C-Projects), so the travis.sh script can be simplified.

I also added separate commits that change the dependency repo to `neovim/deps` and fix inconsistent whitespace/tabs formatting; you can append ?w=1 to the Github URL to compare without these changes (i.e. https://github.com/fwalch/neovim/commit/4734317e23d7eeaf334539fa517b34fa5a29370b?w=1).