Speed up startup time a bit

_collections is the C implementation (and where defaultdict lies), and
is as such already loaded when the interpreter is launched. collections
imports a bunch of other useless stuff we're not interested in.

src/decorators.py

@@ -1,5 +1,5 @@
 import fnmatch
-from collections import defaultdict
+from _collections import defaultdict
 
 import botconfig
 from oyoyo.parse import parse_nick

src/settings.py

@@ -1,4 +1,4 @@
-from collections import defaultdict
+from _collections import defaultdict
 import math
 from src import events
 

src/wolfgame.py

@@ -25,7 +25,7 @@ import botconfig
 import traceback
 from src import decorators
 from datetime import datetime, timedelta
-from collections import defaultdict
+from _collections import defaultdict
 import threading
 import copy
 import time