Updated OpenShift docs to use OpenShift latest Ruby 2.0 Cartridge.

Small update to the OpenShift docs to use OpenShift's latest Ruby 2.0 Cartridge. But OpenShift's Bundler still seems a little old, resulting in some workarounds.
I'd spell out `2` as `two`. Given that change, the wording still sounds a bit off to me. I'd reword this sentence as follows.

    Then change the two gem dependencies below to use hash rocket syntax for the "require" option.