Update .appveyor.yml

[avilchess]

Make sure you have checked all steps below.

Description

• [ ] Here are some details about my PR, including screenshots of any UI changes:

Tests

• [ ] My PR adds the following unit tests OR does not need testing for this extremely good reason:

Benchmarks

• [ ] My PR adds the following micro benchmarks OR does not need benchmarks for this extremely good reason:

Commits

• [ ] My commits have been squashed if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

License

• [ ] Add a Mozilla Public License 2.0 license header to all the new files.

Documentation

• [ ] In case of new functionality, my PR adds documentation that describes how to use it.