Add Java 8 to migration guide
Add Java 8 to migration guide

Fixes #4314.

wegtam/playframework,Shruti9520/playframework,wegtam/playframework,zaneli/playframework,aradchykov/playframework,Shenker93/playframework,Shruti9520/playframework,Shenker93/playframework,ktoso/playframework,rajeshpg/playframework,rajeshpg/playframework,wegtam/playframework,marcospereira/playframework,marcospereira/playframework,mkurz/playframework,benmccann/playframework,wsargent/playframework,Shenker93/playframework,ktoso/playframework,marcospereira/playframework,playframework/playframework,benmccann/playframework,Shenker93/playframework,ktoso/playframework,wsargent/playframework,aradchykov/playframework,rajeshpg/playframework,aradchykov/playframework,mkurz/playframework,mkurz/playframework,playframework/playframework,zaneli/playframework,aradchykov/playframework,rajeshpg/playframework,richdougherty/playframework,Shruti9520/playframework,hagl/playframework,Shruti9520/playframework,wsargent/playframework,marcospereira/playframework,zaneli/playframework,benmccann/playframework,zaneli/playframework,ktoso/playframework,benmccann/playframework,mkurz/playframework,wsargent/playframework,richdougherty/playframework,richdougherty/playframework,hagl/playframework,hagl/playframework,richdougherty/playframework,playframework/playframework,wegtam/playframework,hagl/playframework