[hotfix][docs][py] Fix class name in example

This closes apache#5692.

docs/dev/stream/python.md

@@ -464,15 +464,15 @@ Rich functions (.e.g `RichFilterFunction`) enable to define (override) the optio
 The user may use these functions for initialization and cleanups.
 
 {% highlight python %}
-class Tockenizer(RichMapFunction):
+class Tokenizer(RichMapFunction):
  def open(self, config):
  pass
  def close(self):
  pass
  def map(self, value):
  pass
 
-data_stream.map(Tockenizer())
+data_stream.map(Tokenizer())
 {% endhighlight %}
 
 The `open` function is called by the worker before starting the streaming pipeline.