Update Lookup date only when ShouldExecute is true

[xr1337]

I was reading the class that implements the validation logic to run the rate limit.
While reading the class method below:

private class func shouldExecute(name name: String, limit: NSTimeInterval) -> Bool

I've notice the lookup date is updated regardless if 'should' is true or false.
I would expect the last executed date to be updated when the limit has passed. That way, subsequent request could refer to the original date instead of the last checked date.

Sorry for not making a pull request.

[xr1337]

Closing as i see a pull request that fixes this.