Check out shallow git copies

Since the repositories are throw-away copies, it's not necessary to pull
the entire history.
Merge pull request #22 from passy/shallow-clone

Check out shallow git copies
Add latest binaries to uninstall script
Merge branch 'master' of https://github.com/elm-lang/elm-platform
Revert "Check out shallow git copies"

This reverts commit 8dfecb9bb0c0b1730cc5139d6355aaf13eee9789.

Fix #23
Clone shallow copy for master builds

Follow-up to #24