fix end example

Author: Almenon

README.md

@@ -88,6 +88,7 @@ pyshell.on('message', function (message) {
 
 // end the input stream and allow the process to exit
 pyshell.end(function (err,code,signal) {
+  if (err) throw err;
   console.log('The exit code was: ' + code);
   console.log('The exit signal was: ' + signal);
   console.log('finished');