Remove Berksfile.lock from version control

A bug in Berkshelf 2.x makes this file pretty much useless:
https://github.com/RiotGames/berkshelf/issues/637

The problem might be fixed in Berkshelf 3.x, but this version hasn't
been released yet. Therefore, remove Berksfile.lock to not raise
expectations and confuse people.

This reverts commit 8a28120396319381c64f165aeb86e5b5c4dff211.
Merge pull request #14 from elm-city-craftworks/remove-berksfile-lock

Remove Berksfile.lock from version control