[sphinx cleanup]
Fix sphinx warning introduced by r217537

llvm-svn: 217541
diff --git a/llvm/docs/CodeGenerator.rst b/llvm/docs/CodeGenerator.rst
index 9eb8cf3..b0a1059 100644
--- a/llvm/docs/CodeGenerator.rst
+++ b/llvm/docs/CodeGenerator.rst
@@ -291,7 +291,7 @@
 memory, is commutable, etc), and holds any target-specific flags.
 
 The ``TargetFrameLowering`` class
------------------------------
+---------------------------------
 
 The ``TargetFrameLowering`` class is used to provide information about the stack
 frame layout of the target. It holds the direction of stack growth, the known