process: invoke EventEmitter on `process`

This properly sets the `_maxListeners` property, which
fixes the max listener warning. Closes #4924.

src/node.js

@@ -35,6 +35,7 @@
         value: process.constructor
       }
     });
+    EventEmitter.call(process);
 
     process.EventEmitter = EventEmitter; // process.EventEmitter is deprecated