[Podfile] Check that platforms actually have a deployment target.
[Podfile] Check that platforms actually have a deployment target.

Closes #305.

orta/Core,dacaiguoguogmail/Core,k0nserv/Core,CocoaPods/Core,dnkoutso/Core,Ashton-W/Core,gabro/Core,brianmichel/Core,AdamCampbell/Core