Standardise on sentence case for titles
diff --git a/docs/api-stability.rst b/docs/api-stability.rst
index 6a2e60e..53669b0 100644
--- a/docs/api-stability.rst
+++ b/docs/api-stability.rst
@@ -1,4 +1,4 @@
-API Stability
+API stability
 =============
 
 From its first release, ``cryptography`` will have a strong API stability