### Description
When I was reading the document, I found that some examples had extra
spaces and violated "Unexpected spaces around keyword / parameter equals
(E251)" in pep8. I removed these extra spaces.
### Tag maintainer
@eyurtsev
### Twitter handle
[billvsme](https://twitter.com/billvsme)
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The `CustomOutputParser` needs to throw `OutputParserException` when it
fails to parse the response from the agent, so that the executor can
[catch it and
retry](be9371ca8f/langchain/agents/agent.py (L767))
when `handle_parsing_errors=True`.
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#### Who can review?
Tag maintainers/contributors who might be interested: @hwchase17
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