Revert akka to 7a6dab2319b525e479f6bae735d1d1b2f9efb9ff

It seems like my original guess in #75 was wrong. Some other change in
akka build must have broken community build. Let's revert to the last
akka revision that is known to work before we figure out what happened.
Merge pull request #77 from gkossakowski/akka-revert

Revert akka to 7a6dab2319b525e479f6bae735d1d1b2f9efb9ff