Correct timecodes after one hour
Timecodes after 1 hour were being written incorrectly to .vtt files.
This problem prevented captions from displaying in the browser after the 1 hour mark.
Example: 00:60:55.579 --> 00:60:58.440 A:middle L:90%
instead of the correct: 01:00:55.579 --> 01:00:58.440 A:middle L:90%
This fixes issue #6 (closed) in GitLab.