Update replay_memory.py

When self.size == self._initial_size, ReplayMemory.initialized should be True

Author: Katze2664

mushroom_rl/rl_utils/replay_memory.py

@@ -144,7 +144,7 @@ def initialized(self):
             allows it to be used.
 
         """
-        return self.size > self._initial_size
+        return self.size >= self._initial_size
 
     @property
     def size(self):