Documentation: add a missing word


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170296 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/AutomaticReferenceCounting.rst b/docs/AutomaticReferenceCounting.rst
index 9babf8f..56a922b 100644
--- a/docs/AutomaticReferenceCounting.rst
+++ b/docs/AutomaticReferenceCounting.rst
@@ -8,7 +8,7 @@
     .when-revised { font-weight: bold; font-style: normal; }
 
     /*
-     * Automatic numbering is described this article:
+     * Automatic numbering is described in this article:
      * http://dev.opera.com/articles/view/automatic-numbering-with-css-counters/
      */
     /*