add cJSON, update mosquitto to 1.6.3 and update the makefile

Guo Wenxue

2019-06-24 809c78de808ed5563e9af4a56227965974ec25fa

 apue/2.Socket/socket_client.c

@@ -109,7 +109,8 @@
          }
       }

       //printf("Read %d bytes data from server: '%s'\n", rv, buf);

       sleep(5);
    }