Update copyright headers (#3086)

Added and updated copyright headers.

Added some missing Flow types.

Removed an invalid prop-types import.

plugins/gatsby-source-react-error-codes/gatsby-node.js

@@ -1,3 +1,7 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ */
+
 const request = require('request-promise');
 
 const errorCodesUrl =