Add GWT 2.7.0 on overview page

Change-Id: I91583c75cf2f19083a1f1286336b5b8b67d571e9
diff --git a/src/main/markdown/overview.md b/src/main/markdown/overview.md
index dedda43..a73fd43 100644
--- a/src/main/markdown/overview.md
+++ b/src/main/markdown/overview.md
@@ -52,7 +52,7 @@
   </div>
   <br/>
   <div>
-    <a href="doc/latest/ReleaseNotes.html">What's New in GWT 2.6.1</a>
+    <a href="doc/latest/ReleaseNotes.html">What's New in GWT 2.7.0</a>
   </div>
 </div>