Add JavaScript syntax highlighting

It seems like JavaScript/ES6 is becoming more common for us to run into
in the wild compared to CoffeeScript
with the advent of Babel / transpiling.

Eventually, we'll probably want to remove kchmck/vim-coffee-script.
Users working on CoffeeScript applications would need to move that
plugin into their personal dotfiles.

README.md

@@ -183,8 +183,7 @@ What's in it?
 * Run many kinds of tests [from vim]([https://github.com/janko-m/vim-test)
 * Set `<leader>` to a single space.
 * Switch between the last two files with space-space.
-* Syntax highlighting for CoffeeScript, Textile, Cucumber, Haml, Markdown, and
-  HTML.
+* Syntax highlighting for Markdown, HTML, JavaScript, Ruby, Go, Elixir, more.
 * Use [Ag](https://github.com/ggreer/the_silver_searcher) instead of Grep when
   available.
 * Map `<leader>ct` to re-index [Exuberant Ctags](http://ctags.sourceforge.net/).
@@ -237,7 +236,7 @@ in this project.
 License
 -------
 
-dotfiles is copyright © 2009-2016 thoughtbot. It is free software, and may be
+dotfiles is copyright © 2009-2017 thoughtbot. It is free software, and may be
 redistributed under the terms specified in the [`LICENSE`] file.
 
 [`LICENSE`]: /LICENSE

vimrc.bundles

@@ -41,6 +41,7 @@ Plug 'elixir-lang/vim-elixir'
 Plug 'fatih/vim-go'
 Plug 'janko-m/vim-test'
 Plug 'kchmck/vim-coffee-script'
+Plug 'pangloss/vim-javascript'
 Plug 'pbrisbin/vim-mkdir'
 Plug 'scrooloose/syntastic'
 Plug 'slim-template/vim-slim'