Add warning when using react-error-overlay in production (facebook#3264)

* Add a warning when running minified

* Add more robust check

* Update index.js

Author: Timer

packages/react-error-overlay/src/index.js

@@ -167,3 +167,10 @@ window.__REACT_ERROR_OVERLAY_GLOBAL_HOOK__.iframeReady = function iframeReady()
   isLoadingIframe = false;
   updateIframeContent();
 };
+
+if (process.env.NODE_ENV === 'production') {
+  console.warn(
+    'react-error-overlay is not meant for use in production. You should ' +
+      'ensure it is not included in your build to reduce bundle size.'
+  );
+}