Update TOC to match actual sections

Author: zbynek

src/main/markdown/makinggwtbetter.md

@@ -17,7 +17,7 @@ If you are interested in understanding the internals of Google Web Toolkit (GWT)
     3.  [Testing](#testing)
 4.  [Contributing Code](#contributingcode)
     1.  [Code Style](#codestyle)
-    2.  [Contributor License Agreement](#class)
+    2.  [Unit Testing](#unit-testing)
     3.  [Submitting Patches](#submittingpatches)
     4.  [GWT Committers](#committers)
 5.  [Contributing to Webpage & Documentation](#webpage)