Add JSX syntax plugin

The "mxw/vim-jsx" (1) plugin adds syntax highlighting and indenting
support for JSX. It is not a standalone JavaScript plugin and must be
used with a base JS highlighter and integrates with the currently used
and recommended "pangloss/vim-javascript" (2) plugin (vim-jsx's
"official" dependency).

References:
  (1) https://github.com/mxw/vim-jsx
  (2) https://github.com/pangloss/vim-javascript

GH-44

snowblocks/vim/vimrc

@@ -34,6 +34,7 @@ Plug 'airblade/vim-gitgutter'
 
 "+--- Syntax ---+
 Plug 'pangloss/vim-javascript'
+Plug 'mxw/vim-jsx'
 Plug 'plasticboy/vim-markdown'
 
 "+--- Color Themes ---+