Rename yum::epel to yum-epel because of changes to yum cookbook

I'll be honest, I have no clue if this is even valid, but I do know that the yum::epel cookbook has been split into its own yum-epel cookbook.  When I try to run this cookbook as it is, chef complains that it can't find the epel recipe.  I don't speak ruby and I don't know chef or berkshelf.  I didn't run any tests on this change before submitting this PR.