Use StringBuilder instead of StringBuffer where possible.

Change-Id: Ifc67c84a3e786cd766f45726733a6d294d2652a1
Signed-off-by: Carsten Hammer <carsten.hammer@t-online.de>
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CommitCommandTest.java

@@ -485,7 +485,7 @@ public class CommitCommandTest extends RepositoryTestCase {
 	}
 
 	private static String reflogComments(List<ReflogEntry> entries) {
-		StringBuffer b = new StringBuffer();
+		StringBuilder b = new StringBuilder();
 		for (ReflogEntry e : entries) {
 			b.append(e.getComment()).append(";");
 		}