Update OCMock to v2.2.3

2.2.3 should probably replace 2.2.2, being nothing but a bugfix release, but I'm not sure if CocoaPods policy allows this (or how it would affect existing installations), so I just added the new one to be safe.

Details on the bugfix, from http://ocmock.org/news/

2.2.2:

> New minor release (2.2.2) that brings full support for ARM 64-bit builds on iOS

2.2.3:

> New minor release (2.2.3) that actually includes ARM 64-bit build. No functional changes compared to previous version.