Adapt rubygem-mongo to the new name schema

Use the new schema for rubygem in SLE12 and openSUSE 13.2.
Oh, openSUSE is recognized as a different platform now? (Which is good, but probably breaks all cookbooks ;-)).

Btw, the two lines look the same, so what about doing `if (SLE>=12) or (openSUSE>=13.2)` instead?