should not verify armv7s arch on xcode 6

## motivation

In Xcode 6, armv7s is not a valid architecture.

When the calabash.framework is created, the architectures in the .a are verified.

**NB** This does not _fix_ or _enable_ Xcode 6/iOS 8 testing - it is merely a step along the road.

I don't know what the consequences of dropping armv7s are yet.  It might be that we have to compile and distribute the calabash.framework using Xcode 5.1.1.

## tests

The `make` tests will pass everywhere for Xcode >= 5.0.

The `run-chou-tests.rb` will fail locally on Xcode 6b4.

cc @krukow