Changed open.async to options.async, previously written it was re…

…ferencing the window.open function.

src/ajax.js

@@ -204,7 +204,7 @@
 
       var xhr = self.xhr
 
-      xhr.open(method.toUpperCase(), url, open.async, options.user, options.password)
+      xhr.open(method.toUpperCase(), url, options.async, options.user, options.password)
       if (options.user && 'withCredentials' in xhr) xhr.withCredentials = true
 
       xhr.onreadystatechange = snack.bind(self.onStateChange, self)