Fixing a sphinx warning.

llvm-svn: 248729
diff --git a/clang-tools-extra/docs/modularize.rst b/clang-tools-extra/docs/modularize.rst
index 98bb8a0..9d6170a 100644
--- a/clang-tools-extra/docs/modularize.rst
+++ b/clang-tools-extra/docs/modularize.rst
@@ -210,7 +210,7 @@
 An optional ``-root-module=<root-name>`` option can be used to cause a root module
 to be created which encloses all the modules.
 
-An optional ``-problem-files-list=<problem-file-name> can be used to input
+An optional ``-problem-files-list=<problem-file-name>`` can be used to input
 a list of files to be excluded, perhaps as a temporary stop-gap measure until
 problem headers can be fixed.