Update ftplugin (#553)

* Revert setting 'regexpengine' from filetype plugin

Setting 'regexpengine' from filetype plugin without reenabling syntax
doesn't fix problems described in #88 and #93.  Seems like those
problems are reproducible only in versions 7.4 and 7.4.1.  Those few
unfortunates who encounter it today will be able to find workaround
by reading project issues.

* Move filetype plugin to after directory

- Add dollar sign to 'iskeyword'
- Make use of b:undo_ftplugin variable

Author: dmitrivereshchagin

ftplugin/javascript.vim renamed to after/ftplugin/javascript.vim

@@ -3,8 +3,6 @@
 " Maintainer:   vim-javascript community
 " URL:          https://github.com/pangloss/vim-javascript
 
-setlocal suffixesadd+=.js
+setlocal iskeyword+=$ suffixesadd+=.js
 
-if v:version == 703 && exists('&regexpengine') || v:version == 704 && !has('patch2')
-  set regexpengine=1
-endif
+let b:undo_ftplugin .= ' | setlocal iskeyword< suffixesadd<'