Enabled testing on HHVM on Travis
Enabled testing on HHVM on Travis

aik099/Mink,handrus/Mink,talib570/Mink,jhedstrom/Mink,Chekote/Mink,jordi12100/Mink,stof/Mink,jordi12100/Mink,minkphp/Mink,Behat/Mink,Chekote/Mink,minkphp/Mink,jhedstrom/Mink,talib570/Mink