Remove custom rspec

Use thoughtbot's:

https://github.com/thoughtbot/dotfiles/blob/master/rspec

The only difference was fail-fast, which was not helpful.
Do not enable Syntastic for HTML, Handlebars, etc.
Set up GOROOT
Don't use custom prompt

Use thoughtbot's:

https://github.com/thoughtbot/dotfiles/commit/7dbc8f44a15b768f1dddb4f60b46a851b7f10764
Use NVM for Node
Increase ulimit for Gulp.js