Correct typo in HistogramDiffIndex Javadoc

Change-Id: I8bd2e81fcc14aa86919c504f1d0001944dea50b2
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/diff/HistogramDiffIndex.java

@@ -117,7 +117,7 @@ final class HistogramDiffIndex<S extends Sequence> {
 	 * This allows a chain to terminate with {@code 0}, as {@code 0} would never
 	 * be a valid next element.
 	 *
-	 * The array is sized to be {@code region.getLenghtA()} and element indexes
+	 * The array is sized to be {@code region.getLengthA()} and element indexes
 	 * are converted to array indexes by subtracting {@link #nextShift}, which
 	 * is just a cached version of {@code region.beginA}.
 	 */