Update CDVReachability from Apple's Reachability code

See: https://developer.apple.com/library/ios/samplecode/Reachability/History/History.html#//apple_ref/doc/uid/DTS40007324-RevisionHistory-DontLinkElementID_1

The latest revision lists IPv6 compatibility, but the previous revision was "minor bug fixes". Not sure if these include the IPv6 stuff, but Apple has been rejecting apps if they are not IPv6 compatible, so this would be a risk.