Added cross-env package for windows compatibility

[sammwyy]

Proposed changes

Added cross-env prefix to all environment variables in package.json to ensure compatibility with Windows development.

Types of changes

What types of changes does your code introduce to 7TV? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING doc
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged

Further comments

I would like to contribute to the development of the project, however my work environment is Windows (Weird, I know), and I preferred to do this PR separately rather than leaving it together with a feature PR.

[CLAassistant]

All committers have signed the CLA.

[Excellify]

This should be fine