Bump Bunny to 1.6.3

It's really unfortunate that we only do this after the 1.0 release but better
late than never.
Merge pull request #77 from michaelklishin/patch-4

Bump Bunny to 1.6.3
Merge branch 'master' into sneakers_one_oh
Require forwardable.
Merge pull request #79 from SebastianEdwards/master

Require forwardable.
bump
Merge branch 'master' into sneakers_one_oh