Fixes #1470 by only appending to a Gemfile that exists (dummy doesn't have one).
Fixes #1470 by only appending to a Gemfile that exists (dummy doesn't have one).

johanb/refinerycms,Eric-Guo/refinerycms,LytayTOUCH/refinerycms,trevornez/refinerycms,SmartMedia/refinerycms-with-custom-icons,anitagraham/refinerycms,Retimont/refinerycms,mkaplan9/refinerycms,mojarra/myrefinerycms,mkaplan9/refinerycms,hoopla-software/refinerycms,chrise86/refinerycms,KingLemuel/refinerycms,chrise86/refinerycms,louim/refinerycms,chrise86/refinerycms,KingLemuel/refinerycms,simi/refinerycms,anitagraham/refinerycms,sideci-sample/sideci-sample-refinerycms,Eric-Guo/refinerycms,kappiah/refinerycms,mabras/refinerycms,aguzubiaga/refinerycms,gwagener/refinerycms,LytayTOUCH/refinerycms,bryanmtl/g-refinerycms,mojarra/myrefinerycms,johanb/refinerycms,hoopla-software/refinerycms,bricesanchez/refinerycms,refinery/refinerycms,stefanspicer/refinerycms,trevornez/refinerycms,stefanspicer/refinerycms,kelkoo-services/refinerycms,mlinfoot/refinerycms,kappiah/refinerycms,bryanmtl/g-refinerycms,simi/refinerycms,mlinfoot/refinerycms,kelkoo-services/refinerycms,stefanspicer/refinerycms,kappiah/refinerycms,bricesanchez/refinerycms,louim/refinerycms,sideci-sample/sideci-sample-refinerycms,simi/refinerycms,Retimont/refinerycms,SmartMedia/refinerycms-with-custom-icons,LytayTOUCH/refinerycms,refinery/refinerycms,mobilityhouse/refinerycms,Retimont/refinerycms,gwagener/refinerycms,aguzubiaga/refinerycms,refinery/refinerycms,johanb/refinerycms,mabras/refinerycms,mkaplan9/refinerycms,anitagraham/refinerycms,simi/refinerycms,mlinfoot/refinerycms,KingLemuel/refinerycms,Eric-Guo/refinerycms,hoopla-software/refinerycms,mabras/refinerycms,gwagener/refinerycms,trevornez/refinerycms,aguzubiaga/refinerycms,mobilityhouse/refinerycms