Track Google analytic Timing Event

In the header ```GAIDictionaryBuilder.h``` of **Google Analytics iOS SDK v3**, it indicates that users should pass ```intervalMillis``` as time interval argument. (i.e. seconds in millisecond).
So this pull request first make the ```interval``` NSNumber object into double and multiplies 1000 to get milliseconds.

Second, the upstream implementation of ```Providers/GoogleAnalyticsProvider.m``` overrode wrong method when sending timing event.
In ```+ [ARAnalytics finishTimingEvent:withProperties:]```, it calls ```-[ARAnalyticalProvider logTimingEvent:withInterval:properties]```, but the ```GoogleAnalyticsProvider.m``` overrides ```logTimingEvent:withInterval:```. This makes the implementation of ```GoogleAnalyticsProvider``` never called.