Add empty mock for dgram (facebook#2600)

Author: micopiira

packages/react-scripts/config/webpack.config.dev.js

@@ -275,6 +275,7 @@ module.exports = {
   // Some libraries import Node modules but don't use them in the browser.
   // Tell Webpack to provide empty mocks for them so importing them works.
   node: {
+    dgram: 'empty',
     fs: 'empty',
     net: 'empty',
     tls: 'empty',

packages/react-scripts/config/webpack.config.prod.js

@@ -341,6 +341,7 @@ module.exports = {
   // Some libraries import Node modules but don't use them in the browser.
   // Tell Webpack to provide empty mocks for them so importing them works.
   node: {
+    dgram: 'empty',
     fs: 'empty',
     net: 'empty',
     tls: 'empty',