Fix library failing to link when compiling app for armv7s.

Xcode 6 changes the standard architectures to exclude armv7s — the instruction set used by the iPhone 5, 5C and iPad 4, which is a variant of the armv7 instruction set. [Read more on Apple’s developer forums](https://devforums.apple.com/thread/244407).

UserVoice uses the standard architectures, so fails to link if a user of the library is compiling for armv7s.

As a library, UserVoice ought to include as many architectures as possible to accommodate the applications linking with it. This pull request changes the UserVoice project to explicitly specify architectures to add armv7s.