Fix pylint errors

Author: tekktrik

adafruit_itertools/__init__.py

@@ -265,7 +265,7 @@ class groupby:
     def __init__(self, iterable, key=None):
         if key is None:
             key = lambda x: x
-        self.keyfunc = key
+        self.keyfunc = key if key is not None else lambda x: x
         self.it = iter(iterable)
         self.tgtkey = self.currkey = self.currvalue = object()