Fix UnifiedJedis pexpireAt glitch

One of the versions of UnifiedJedis.pexpireAt methods is calling the
wrong method on CommandObjects.

src/main/java/redis/clients/jedis/UnifiedJedis.java

@@ -457,7 +457,7 @@ public long pexpireAt(byte[] key, long millisecondsTimestamp) {
 
   @Override
   public long pexpireAt(byte[] key, long millisecondsTimestamp, ExpiryOption expiryOption) {
-    return executeCommand(commandObjects.expireAt(key, millisecondsTimestamp, expiryOption));
+    return executeCommand(commandObjects.pexpireAt(key, millisecondsTimestamp, expiryOption));
   }
 
   @Override