Use future annotations to allow import on desktop computers

I needed this so that I could use `adafruit_hid.keycode.Keycode` in some
programs to help generate keycode lists on my real computer.

Author: jepler

adafruit_hid/__init__.py

@@ -18,6 +18,8 @@
 """
 
 # imports
+from __future__ import annotations
+
 try:
     from typing import Sequence
     import usb_hid