Allow emoji in config file in Windows by always opening it as unicode

[micahellison]

Fixes #1162. I forced utf-8 encoding on open, since apparently Python won't use that in Windows by default.

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have tested this code locally.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.
• All tests pass.

[wren]

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