~/.vimrc: Add handy bindings for ternjs.vim.

Of these, `cw` is kind of troubling, because it also tries to "rename"
non-variables (e.g. in strings or comments).

.vimrc

@@ -24,6 +24,10 @@ if isdirectory($HOME . '/.vim/bundle/vundle')
	Bundle 'terryma/vim-multiple-cursors'
	Bundle 'marijnh/tern_for_vim'
	au FileType javascript nnoremap <buffer> gd :TernDef<cr>
	au FileType javascript nnoremap <buffer> gu :TernRefs<cr>
	au FileType javascript nnoremap <buffer> gt :TernType<cr>
	au FileType javascript nnoremap <buffer> cw :TernRename<cr>
endif
" Have syntax highlighting and non-vi features