Update content-script.js

[robertjcolley]

I tend to navigate directly to https://www.youtube.com (without the backslash) which doesn't match this regex. I've updated it to match an optional backslash. PoC here: https://www.regextester.com/?fam=126957

[lawrencehook]

@robertjcolley Oh nice, thanks!

During my testing, the string in location.href always has a trailing backslash, but your change can't hurt to add.