title: How to run package.json postinstall script only on macOS
body: <p>I have to execute this <code>postinstall</code> script on MacOS (to fix a temporary bug in react-native-maps):</p>
  
  <pre><code>"scripts": {
    "postinstall": "sed -i '' '/Google.*\\.[h|m]/d' node_modules/react-native-maps/lib/ios/AirMaps.xcodeproj/project.pbxproj"
  }
  </code></pre>
  
  <p>It is not needed on Linux or Windows so how can I execute it only on macOS?</p>