IndexDiff: Correct Javadoc for getUntracked() method

Change-Id: I5f26c40dec5f0e4a47413af033dbedb0c252dd20
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/lib/IndexDiff.java

 	}
 
 	/**
-	 * @return list of files on modified on disk relative to the index
+	 * @return list of files that are not ignored, and not in the index.
 	 */
 	public Set<String> getUntracked() {
 		return untracked;