grouping identifier validation fixed

[Minor] Composer version alias bump

[bc] 3x image support

Merge pull request eymengunay#59 from mahemrai/master

PassInvalidException now returns an exception message

Add validation when packaging a pass using the PassValidator class

Changed composer requirement back to PHP 5.3 to support semantic vers…

…ioning of patch release.

Added end of PHP 5.3 support to readme.

Merge pull request eymengunay#35 from chapsuk/master

Added associatedStoreIdentifiers field Pass::toArray result

Merge pull request eymengunay#24 from eymengunay/patch-1

[Minor] Indentation fix

[Minor] Author updated