Update rmagick

Impossible to install the old version on my computer. Need to install it fix the bug.
Replace Memcache (Couchbase memcached) vendor

Memcache has been shutdown yesterday and breaks the app.
Memcachier is a memecache vendor available on heroku.  Replace the old vendor by a new one.
 - [Heroku doc](https://devcenter.heroku.com/articles/memcachier#ruby)
 - [Memcachier gem](https://github.com/memcachier/memcachier-gem)
Use memcachier to handle the config.
Merge branch 'master' of github.com:soundcloud/waveformjs