Modify the Timer for returning correct running time with Timer.ms

I change the Timer class because the property "ms" don't handle the pause and resume time.

Example before: 
timer.repeat( 20000, 1, this.callback, this );
At 5000 : timer.pause(); console.log( timer.ms ); //Output 5000
Wait 3000 : timer.resume(); console.log( timer.ms ); //Ouput 8000 

Example after:
timer.repeat( 20000, 1, this.callback, this );
At 5000 : timer.pause(); console.log( timer.ms ); //Output 5000
Wait 3000 : timer.resume(); console.log( timer.ms ); //Ouput 5000