Only load Virtualenv plugin for python files.

Since Virtualenv is only used for python project (at least for me) it doesn't
make sense to load that plugin when I'm not editing a python file.

Author: Townk

vimrc

@@ -97,7 +97,7 @@ silent! if plug#begin('~/.vim/plugged')
     Plug 'junegunn/vim-github-dashboard' " Github dashboard integration
     Plug 'glts/vim-textobj-comment' " add ic, ac and aC for comment text objects
     Plug 'davidhalter/jedi-vim', { 'for': 'python' } " Python completion
-    Plug 'jmcantrell/vim-virtualenv' " Plugin to make Vim recognize the virtualenv it's being running into
+    Plug 'jmcantrell/vim-virtualenv', { 'for': 'python' } " Plugin to make Vim recognize the virtualenv it's being running into
     Plug 'sukima/xmledit' " xml like helpers
     " Plug 'Shougo/neocomplete.vim'