[SPARK-19574][ML][DOCUMENTATION] Fix Liquid Exception: Start indices amount is...

[SPARK-19574][ML][DOCUMENTATION] Fix Liquid Exception: Start indices amount is not equal to end indices amount

### What changes were proposed in this pull request?
```
Liquid Exception: Start indices amount is not equal to end indices amount, see /Users/xiao/IdeaProjects/sparkDelivery/docs/../examples/src/main/java/org/apache/spark/examples/ml/JavaTokenizerExample.java. in ml-features.md
```

So far, the build is broken after merging https://github.com/apache/spark/pull/16789

This PR is to fix it.

## How was this patch tested?
Manual

Author: Xiao Li <gatorsmile@gmail.com>

Closes #16908 from gatorsmile/docMLFix.

examples/src/main/java/org/apache/spark/examples/ml/JavaTokenizerExample.java

@@ -39,7 +39,7 @@ import org.apache.spark.sql.types.StructType;
 // col("...") is preferable to df.col("...")
 import static org.apache.spark.sql.functions.callUDF;
 import static org.apache.spark.sql.functions.col;
-// $example off
+// $example off$
 
 public class JavaTokenizerExample {
   public static void main(String[] args) {