Add type hint for DCMotor.__exit__() traceback argument

Author: tekktrik

adafruit_motor/motor.py

@@ -22,6 +22,7 @@
 
 try:
     from typing import Optional, Type
+    from types import TracebackType
     from pwmio import PWMOut
 except ImportError:
     pass
@@ -115,5 +116,5 @@ def decay_mode(self, mode: int = FAST_DECAY):
     def __enter__(self):
         return self
 
-    def __exit__(self, exception_type: Optional[Type[type]], exception_value: Optional[BaseException], traceback): # TODO: Add traceback typing
+    def __exit__(self, exception_type: Optional[Type[type]], exception_value: Optional[BaseException], traceback: Optional[TracebackType]):
         self.throttle = None