RefSpec: add missing @since

New API needs an @since 6.2 annotation.

Change-Id: I16b01ea820cc651605166acc13591b515541d06b
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit/src/org/eclipse/jgit/transport/RefSpec.java

@@ -320,6 +320,7 @@ public boolean isWildcard() {
 	 * Check if this specification is a negative one.
 	 *
 	 * @return true if this specification is negative.
+	 * @since 6.2
 	 */
 	public boolean isNegative() {
 		return negative;