Update rails_bootstrap_navbar to avoid a bug

See bootstrap-ruby/bootstrap-navbar@5d70237d510d1749552a41156d9288bfc6486316
This was causing problems, so updated to v2 or newer
Forgot how Gemfiles work
Match up navbar width with the rest of the page

Work on #53
Merge pull request #58 from kotct/navbar-width

Navbar width fix (#53)