[doc] Incorrect picture in pulsar function-overview

[huangdx0726]

Describe the bug
Incorrect picture in pulsar function-overview.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'http://pulsar.apache.org/docs/en/2.4.2/functions-overview'
2. Click on '....'
3. Scroll down to 'Programming model'
4. See error

Expected behavior
The last "in" should is "pudding".

Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS]

Additional context
Add any other context about the problem here.