Fix code block, force Sphinx update on RTD.

adafruit_led_animation/group.py

@@ -44,7 +44,7 @@ class AnimationGroup:
 
     Example:
 
-        .. code-block::
+        .. code-block:: python
 
             import board
             import neopixel

docs/requirements.txt

@@ -0,0 +1,5 @@
+# SPDX-FileCopyrightText: 2021 Kattni Rembor for Adafruit Industries
+#
+# SPDX-License-Identifier: Unlicense
+
+sphinx>4