[Test Commit] Fix typo in diagtool.rst

Test commit after obtaining commit access.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369148 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CommandGuide/diagtool.rst

@@ -9,7 +9,7 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
-:program:`diagtool` is a combination of four tool for dealing with diagnostics in :program:`clang`.
+:program:`diagtool` is a combination of four tools for dealing with diagnostics in :program:`clang`.
 
 SUBCOMMANDS
 -----------