Fixes a compatibility issue in FDDeclaredProperty

FDDeclaredProperty was using `- (BOOL)containsString:aString` to determine if a string contained quotes.
This API was introduced in OS X 10.10 and iOS 8 so its usage was causing crashes on older OS Versions.
Merge pull request #3 from tapi/iOS7-compatibility-issue

Removed iOS 8 API call from FDDeclaredProperty.