Remove trailing nulls from id3v1 strings in ParseTag()

[viking]

[mikkyang]

There's a strings package implementation of the null removal you might want to look at here.

Also is there a reason you used an anonymous struct instead of v1.Tag?

[viking]

I didn't know about strings.TrimRight, thanks. Also I'm not sure why I used an anonymous struct in the tests. Fixed both of those.

[viking]

I have fixed the issue that was causing Travis build to fail.

[viking]

The current error is caused because of Travis not being able to build Go itself from the tip branch. All other versions pass.

[frodeaa]

we have the same problem with trailing nulls in v2.TextFrame