Make 2.6 the default server profile for the test suite too.
Make 2.6 the default server profile for the test suite too.

We leave 2.4 for Travis CI since their CI environment uses Redis 2.4.

[ci skip]

RedisLabs/predis,johnhelmuth/predis,nguyenthaihan/predis,SwelenFrance/predis,vend/predis,moria/predis,RudyJessop/predis,protomouse/predis,mrkeng/predis,quangnguyen90/predis,lvbaosong/predis,CloudSide/predis,dzung2t/predis,zhangyancoder/predis,WalterShe/predis,dominics/predis,nrk/predis,channelgrabber/predis,SecureCloud-biz/predis,gencer/predis,stokes3452/predis,gopalindians/predis,oswaldderiemaecker/predis