HADOOP-1066 omission: Added missing word 'that' to website

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/trunk@575876 13f79535-47bb-0310-9956-ffa450edef68

docs/index.html

@@ -185,7 +185,7 @@ document.write("Last Published: " + document.lastModified);
 </div>
     
 <p>
-    Hadoop is a software platform lets one easily write and run
+    Hadoop is a software platform that lets one easily write and run
     applications that process vast amounts of data.</p>