update scala 2.11.2 and akka 2.3.6

- Scala 2.11.1 has several issues in the collections library.
- Akka 2.3.5 was released for Scala 2.10.4 and 2.11.2
Merge pull request #121 from tsuyoshizawa/master

update scala 2.11.2 and akka 2.3.6