Commit: Use Repository.newObjectInserter

Everyone else does.  This must have been a spot I missed during
some sort of squash while developing the series.

Change-Id: I62eae50b618f47ee33ad7cf71fc05b724f603201
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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

@@ -339,7 +339,7 @@ public class Commit implements Treeish {
 	public void commit() throws IOException {
 		if (getCommitId() != null)
 			throw new IllegalStateException(MessageFormat.format(JGitText.get().commitAlreadyExists, getCommitId()));
-		ObjectInserter odi = objdb.getObjectDatabase().newInserter();
+		ObjectInserter odi = objdb.newObjectInserter();
 		try {
 			ObjectId id = odi.insert(Constants.OBJ_COMMIT, odi.format(this));
 			odi.flush();