"Fixed" the clean-regex (scanner) to make it handle square brackets correctly.

This pull request is related to [issue #2639](https://github.com/RuudBurger/CouchPotatoServer/issues/2639).
The scanner couldn't find the right movie results in some cases because it didn't handle square brackets correctly.

**I fixed it by adjusted the "clean-regex" (in [core/plugins/scanner/main.py](https://github.com/RuudBurger/CouchPotatoServer/blob/master/couchpotato/core/plugins/scanner/main.py)).**