Added chmod to 644 for subtitles

[hp197]

Description

I ran into problems with permissions. Default subliminal write files with 0600 permission.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] I have based this change on the nightly branch
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas

[clinton-hall]

Thanks. I just merged in to nightly branch. I expect to merge up to master soon.