Preparing for 2.7.0 development: Fixing hadoop-project/src/site/apt/index.apt.vm

to point to 2.6.0 as the last stable release.

hadoop-project/src/site/markdown/index.md.vm

@@ -16,7 +16,7 @@ Apache Hadoop ${project.version}
 ================================
 
 Apache Hadoop ${project.version} is a minor release in the 2.x.y release
-line, building upon the previous stable release 2.4.1.
+line, building upon the previous stable release 2.6.0.
 
 Here is a short overview of the major features and improvements.