Fix Stderr going to Stdout

Closes #61

Author: mattlyons0

rsync.js

@@ -472,7 +472,7 @@ Rsync.prototype.output = function(stdout, stderr) {
         this._outputHandlers.stdout = stdout;
     }
     if (typeof(stderr) === 'function') {
-        this._outputHandlers.stderr = stdout;
+        this._outputHandlers.stderr = stderr;
     }
 
     return this;