Emit error on correct stream

This change fixes one of the issues from #98. `state.stream` can be the wrong stream to emit an error to if no path is passed however `ret` will always be the right stream to emit to. 

This makes it possible to listen for 'error' events although an error is still squelched if it's not listened for.

index.js

@@ -232,7 +232,7 @@ function Xray() {
       }
 
       node(function(err) {
-        if (err) state.stream.emit('error', err);
+        if (err) ret.emit('error', err);
       })
 
       return ret;