Update cli.py: encoding='utf-8'

[BaseMax]

The issue happened in our project at SalamLang/Salam#265 in pre-commit for lining YAML files.

UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 445: character maps to

[coveralls]

coverage: 99.825%. remained the same
when pulling 6ca01fe on MaxFork:supports-utf8
into 95e17b3 on adrienverge:master.

[BaseMax]

cc @adrienverge @jbampton

[adrienverge]

Hello and thanks for the proposal. Could you check out other pull requests related to character encoding? How does this one differ from them?

[BaseMax]

Hi @adrienverge, happy connecting.

There are total 3 merge requests related to encoding.
1- #630
2- #240
3- #696 (CURRENT MERGE REQUEST)

The https://github.com/adrienverge/yamllint/pull/630/files#diff-2e0288fc9fc3cda09f90a25f76bedb9ce0cea019d01147b436e575c71a3e674eR222 merge request looks fine but it doesn't have the change I applied.

My problem is that I have Persian UTF8 text in my YAML files and the problem was related to the 'cli.py' file.

Related to my issue https://github.com/adrienverge/yamllint/pull/240/files looks like a good patch as it can automatically detect the encoding and then use that in reading the file but I can see your comments there and it seems you are not happy to add new dependencies. Q: "I'm very against adding dependencies (like chardet)."