Fix display_name casing for reinforcement-learning topic

Author: Tariolle

topics/reinforcement-learning/index.md

@@ -1,5 +1,5 @@
 ---
-display_name: Reinforcement Learning
+display_name: Reinforcement learning
 short_description: Reinforcement learning is a machine learning paradigm focused on sequential decision-making, in which an autonomous agent learns optimal behavior by interacting with a dynamic environment to maximize cumulative reward signals.
 topic: reinforcement-learning
 wikipedia_url: https://en.wikipedia.org/wiki/Reinforcement_learning