the target of the link uses the singular form, so do we too

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112367 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/www/menu.html.incl b/www/menu.html.incl
index 35e67d0..d828449 100644
--- a/www/menu.html.incl
+++ b/www/menu.html.incl
@@ -8,7 +8,7 @@
     <a href="/index.html">About</a>
     <a href="/features.html">Features</a>
     <a href="/comparison.html">Comparisons</a>
-    <a href="/docs/UsersManual.html">Users' Manual</a>
+    <a href="/docs/UsersManual.html">User's Manual</a>
     <a href="/compatibility.html">Language&nbsp;Compatibility</a>
     <a href="/docs/LanguageExtensions.html">Language&nbsp;Extensions</a>
     <a href="/cxx_status.html">C++ Status</a>