Make PHP 5.5 the minimum supported version
Make PHP 5.5 the minimum supported version

Also update all other composer requirements to the "^" syntax.

dopesong/Slim,akrabat/Slim,iinux/Slim,Sam-Burns/Slim,slimphp/Slim,RealSelf/Slim,designermonkey/Slim,samsonasik/Slim,iinux/Slim,AndrewCarterUK/Slim,juliangut/Slim,feryardiant/slim,mnapoli/Slim,jaapverloop/Slim,iinux/Slim,JoeBengalen/Slim,foxyantho/Slim