encoding='utf-8' for reading contracts

[Hecate2]

What I did

On Windows without utf-8 encoding by default, there can be errors like UnicodeDecodeError: 'gbk' codec can't decode byte 0x80 in position 52: illegal multibyte sequence when contracts are being read. Related issue: None

How I did it

Using encoding='utf-8' for contracts

How to verify it

I cloned https://github.com/RockX-SG/stake and made brownie work with the contracts on Windows 10.

Checklist

• [x] I have confirmed that my PR passes all linting checks
• [ ] I have included test cases
• [ ] I have updated the documentation
• [x] I have added an entry to the changelog

[iamdefinitelyahuman]

Pretty straightforward fix, thanks