Shim child_process

See facebook#3033

Author: andreypopp

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

@@ -257,6 +257,7 @@ module.exports = {
   node: {
     fs: 'empty',
     net: 'empty',
-    tls: 'empty'
+    tls: 'empty',
+    child_process: 'empty'
   }
 };

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

@@ -290,6 +290,7 @@ module.exports = {
   node: {
     fs: 'empty',
     net: 'empty',
-    tls: 'empty'
+    tls: 'empty',
+    child_process: 'empty'
   }
 };