Upgrade akka (#8260)
Upgrade akka (#8260)

https://akka.io/blog/news/2018/02/28/akka-2.5.11-released
playframework/playframework,Shenker93/playframework,mkurz/playframework,Shenker93/playframework,Shenker93/playframework,marcospereira/playframework,wegtam/playframework,benmccann/playframework,marcospereira/playframework,mkurz/playframework,benmccann/playframework,playframework/playframework,Shenker93/playframework,wegtam/playframework,wegtam/playframework,mkurz/playframework,marcospereira/playframework,marcospereira/playframework,playframework/playframework,wegtam/playframework,benmccann/playframework,benmccann/playframework,mkurz/playframework