Remove unused MutableMapping import from markov.py

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

plugins/markov.py

@@ -6,7 +6,7 @@ from pathlib import Path
 import pickle
 import random
 import shutil
-from typing import Any, List, MutableMapping, Sequence
+from typing import Any, List, Sequence
 
 from asyncirc.protocol import IrcProtocol
 from irclib.parser import Prefix