Add missing '@Override' annotations.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1725779 13f79535-47bb-0310-9956-ffa450edef68

httpclient/src/main/java/org/apache/hc/client5/http/auth/KerberosCredentials.java

@@ -58,10 +58,12 @@ public class KerberosCredentials implements Credentials, Serializable {
         return gssCredential;
     }
 
+    @Override
     public Principal getUserPrincipal() {
         return null;
     }
 
+    @Override
     public char[] getPassword() {
         return null;
     }