message: readme: Rename OS X to macOS.
diff: @@ -20,7 +20,7 @@ If your distribution did not come with Python3 and *pip* for Python3, install th
  sudo apt-get install python3 python3-pip
  ```
  -**OS X:**
  +**macOS:**
  Python3 can be installed using [homebrew](http://brew.sh).
  ```bash
  