tispark: remove evil word 'slave' (pingcap#3543)

Co-authored-by: TomShawn <[email protected]>

Author: Joyinqin

tispark-overview.md

@@ -110,17 +110,17 @@ cd $SPARKPATH
 ./sbin/start-master.sh
 ```
 
-After the above step is completed, a log file will be printed on the screen. Check the log file to confirm whether the Spark-Master is started successfully. You can open the [http://spark-master-hostname:8080](http://spark-master-hostname:8080) to view the cluster information (if you does not change the Spark-Master default port number). When you start Spark-Slave, you can also use this panel to confirm whether the Slave is joined to the cluster.
+After the above step is completed, a log file will be printed on the screen. Check the log file to confirm whether the Spark-Master is started successfully. You can open the [http://spark-master-hostname:8080](http://spark-master-hostname:8080) to view the cluster information (if you does not change the Spark-Master default port number). When you start Spark-Worker, you can also use this panel to confirm whether the Worker is joined to the cluster.
 
-#### Start a Slave node
+#### Start a Worker node
 
-Similarly, you can start a Spark-Slave node with the following command:
+Similarly, you can start a Spark-Worker node with the following command:
 
 ```sh
 ./sbin/start-slave.sh spark://spark-master-hostname:7077
 ```
 
-After the command returns, you can see if the Slave node is joined to the Spark cluster correctly from the panel as well. Repeat the above command at all Slave nodes. After all Slaves are connected to the master, you have a Standalone mode Spark cluster.
+After the command returns, you can see if the Worker node is joined to the Spark cluster correctly from the panel as well. Repeat the above command at all Worker nodes. After all Workers are connected to the master, you have a Standalone mode Spark cluster.
 
 #### Spark SQL shell and JDBC server