The hours are not required on the webvtt format

According to http://dev.w3.org/html5/webvtt/ the hours are not required on the webvtt format.

Just make it optional in the regex and update the index in the code.
Also the line with the 'number' before the time is not required.

So support 4 combination of webvtt format: 

1)
00:11.000 --> 00:13.000
<v Roger Bingham>We are in New York City

2)
1
00:11.000 --> 00:13.000
<v Roger Bingham>We are in New York City

3)
00:00:11.000 --> 00:00:13.000
<v Roger Bingham>We are in New York City

4)
1
00:00:11.000 --> 00:00:13.000
<v Roger Bingham>We are in New York City