Update Ruby from 2.2 to 2.2.6
Update Ruby from 2.2 to 2.2.6

"2.2" means "2.2.0" on Travis CI.
ref: https://travis-ci.org/errbit/errbit/jobs/181392638

And it is too older to break build.

ninech/errbit,stevecrozz/errbit,stevecrozz/errbit,wombatsecurity/errbit,wombatsecurity/errbit,rud/errbit,mak-it/errbit,micred/errbit,openSUSE/errbit,mak-it/errbit,threatsim/errbit,disvelop/errbit,jordoh/errbit,stevecrozz/errbit,dwilkie/errbit,ninech/errbit,ninech/errbit,wombatsecurity/errbit,cognoa/errbit,mikk150/errbit,diowa/errbit,errbit/errbit,threatsim/errbit,mikk150/errbit,openSUSE/errbit,Cloud-Temple/errbit,micred/errbit,wombatsecurity/errbit,iFixit/errbit,errbit/errbit,iFixit/errbit,dwilkie/errbit,threatsim/errbit,jordoh/errbit,mikk150/errbit,diowa/errbit,cognoa/errbit,iFixit/errbit,errbit/errbit,micred/errbit,dwilkie/errbit,threatsim/errbit,disvelop/errbit,cognoa/errbit,jordoh/errbit,disvelop/errbit,rud/errbit,bonanza-market/errbit,Cloud-Temple/errbit,rud/errbit,mak-it/errbit,bonanza-market/errbit,bonanza-market/errbit,diowa/errbit,Cloud-Temple/errbit,openSUSE/errbit