Make the CLI work again

[Neurone]

Description

This PR makes the CLI work again, and in particular:

• Switched to the official DeepL Node module
• Added support for API key, via option or via environmental variable
• Upgraded dependencies

Fixes: #2 #3 #4 #5 #7

Types of changes

• 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)

Pull request checklist

• Make sure the commit messages are in (conventional commit style) so a changelog can be (automatically generated).
• Make sure your changes do not fail linting checks (prettier) nor unit test.
• Make sure the coverage remains at 100% and write additional tests if needed.
• Make sure to update the README if necessary