Make constant static in RebuildCommitGraph

Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/debug/RebuildCommitGraph.java

@@ -96,7 +96,7 @@
  * <p>
  */
 class RebuildCommitGraph extends TextBuiltin {
-	private final String REALLY = "--destroy-this-repository";
+	private static final String REALLY = "--destroy-this-repository";
 
 	@Option(name = REALLY, usage = "usage_approveDestructionOfRepository")
 	boolean really;