KAFKA-5918: Fix minor typos and errors in the Kafka Streams turotial

I found several minor issues with the Kafka Streams tutorial:
* Some typos
  * "As shown above, it illustrate that the constructed ..." instead of "As shown above, it illustrate_s_ that the constructed ..."
  * "same as Pipe.java below" instead of "same as Pipe.java _above_"
  * Wrong class name in the `LineSplit` example
* Incorrect imports for the code examples
  * Missing `import org.apache.kafka.streams.kstream.KStream;` in `LineSplit` and `WordCount` example
* Unnecessary (and potentially confusing) split by whitespaces in the `WorkCount` class (the split into words happened already in `LineSplit`)

Author: Jakub Scholz <www@scholzj.com>

Reviewers: Matthias J. Sax <matthias@confluent.io>, Guozhang Wang <wangguoz@gmail.com>

Closes #3883 from scholzj/stream-tutorial-typos

docs/streams/tutorial.html

@@ -186,7 +186,7 @@
     </pre>
 
     <p>
-        As shown above, it illustrate that the constructed topology has two processor nodes, a source node <code>KSTREAM-SOURCE-0000000000</code> and a sink node <code>KSTREAM-SINK-0000000001</code>.
+        As shown above, it illustrates that the constructed topology has two processor nodes, a source node <code>KSTREAM-SOURCE-0000000000</code> and a sink node <code>KSTREAM-SINK-0000000001</code>.
         <code>KSTREAM-SOURCE-0000000000</code> continuously read records from Kafka topic <code>streams-plaintext-input</code> and pipe them to its downstream node <code>KSTREAM-SINK-0000000001</code>;
         <code>KSTREAM-SINK-0000000001</code> will write each of its received record in order to another Kafka topic <code>streams-pipe-output</code>
         (the <code>--&gt;</code> and <code>&lt;--</code> arrows dictates the downstream and upstream processor nodes of this node, i.e. "children" and "parents" within the topology graph).
@@ -320,7 +320,7 @@
     </p>
 
     <pre class="brush: java;">
-        public class Pipe {
+        public class LineSplit {
 
             public static void main(String[] args) throws Exception {
                 Properties props = new Properties();
@@ -405,6 +405,7 @@
         import org.apache.kafka.streams.StreamsBuilder;
         import org.apache.kafka.streams.StreamsConfig;
         import org.apache.kafka.streams.Topology;
+        import org.apache.kafka.streams.kstream.KStream;
 
         import java.util.Arrays;
         import java.util.Properties;
@@ -429,7 +430,7 @@
                 final KafkaStreams streams = new KafkaStreams(topology, props);
                 final CountDownLatch latch = new CountDownLatch(1);
 
-                // ... same as Pipe.java below
+                // ... same as Pipe.java above
             }
         }
     </pre>
@@ -566,6 +567,7 @@
         import org.apache.kafka.streams.StreamsBuilder;
         import org.apache.kafka.streams.StreamsConfig;
         import org.apache.kafka.streams.Topology;
+        import org.apache.kafka.streams.kstream.KStream;
 
         import java.util.Arrays;
         import java.util.Locale;
@@ -593,7 +595,7 @@
                 final KafkaStreams streams = new KafkaStreams(topology, props);
                 final CountDownLatch latch = new CountDownLatch(1);
 
-                // ... same as Pipe.java below
+                // ... same as Pipe.java above
             }
         }
     </pre>