Fix ProtectedMembersInFinalClass warning flagged by error prone

Running recent error prone version complaining on that code:

CharacterHead.java:22: error: [ProtectedMembersInFinalClass] Make
members of final classes package-private: <init>
	protected CharacterHead(char expectedCharacter) {
	          ^
    (see https://errorprone.info/bugpattern/ProtectedMembersInFinalClass)
  Did you mean 'CharacterHead(char expectedCharacter) {'

Bug: 562756
Change-Id: Ic46a0b07e46235592f6e63db631f583303420b73
Signed-off-by: David Ostrovsky <david@ostrovsky.org>

org.eclipse.jgit/src/org/eclipse/jgit/fnmatch/CharacterHead.java

@@ -19,7 +19,7 @@ final class CharacterHead extends AbstractHead {
 	 * @param expectedCharacter
 	 *            expected {@code char}
 	 */
-	protected CharacterHead(char expectedCharacter) {
+	CharacterHead(char expectedCharacter) {
 		super(false);
 		this.expectedCharacter = expectedCharacter;
 	}