Upgrade VimR to 0.1.6

Thank you for the contribution. It will be merged in [a different pull request](https://github.com/caskroom/homebrew-cask/pull/5785) due to some simple recommended alterations. Your contribution is still included (and still credited to you), with the appropriate modifications, when applicable.

Changes:
+ [Facilitated future updates](https://github.com/caskroom/homebrew-cask/pull/4910).