Update Dockerfile (#1369)
Update Dockerfile (#1369)

Update docker image from ruby 2.5.1-alpine to match app.json ruby version
errbit/errbit,diowa/errbit,errbit/errbit,micred/errbit,openSUSE/errbit,micred/errbit,openSUSE/errbit,mak-it/errbit,cognoa/errbit,disvelop/errbit,diowa/errbit,errbit/errbit,mak-it/errbit,openSUSE/errbit,micred/errbit,cognoa/errbit,disvelop/errbit,mak-it/errbit,cognoa/errbit,diowa/errbit,disvelop/errbit