fix serial cmd

raspberry/roberto/Serial.py

@@ -49,8 +49,8 @@ class Serial(object):
                 if data:
                     print(data)
                     command = data[0]
-                    argument = data[2:]
-                    if command in data:
+                    argument = data[2:].strip()
+                    if isalnum(command) and command in self._callbacks:
                         cb = self._callbacks[command]
                         if cb:
                             cb(argument)