Add `/dist` directory to `Makefile`.
Add `/dist` directory to `Makefile`.

Summary: Ignores packaging artifacts from repository consideration.

Reviewers: jeff, tail

Reviewed By: tail

Differential Revision: http://phabricator.local.disqus.net/D18045

disqus/pgshovel,fuziontech/pgshovel,fuziontech/pgshovel,disqus/pgshovel,fuziontech/pgshovel