Add file associations for "vimrc"
Add file associations for "vimrc"

The `vimrc` (1) of Vim (2) was not detected as Vim script syntax,
therefore a association has been added to map it to the `viml` syntax
type provided by the vscode-viml-syntax (3) extension that was added
in GH-184.

References:
  (1) http://vimdoc.sourceforge.net/htmldoc/starting.html#vimrc
  (2) https://www.vim.org
  (3) https://marketplace.visualstudio.com/items?itemName=dunstontc.viml

Resolves GH-191

arcticicestudio/igloo,arcticicestudio/igloo,arcticicestudio/igloo