Fix header level for 'Constants' section of math.rst
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index d59296a..d44b34d 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -277,7 +277,7 @@
 
 
 Constants
-=========
+---------
 
 .. data:: pi