Resolve error in StructuredOutputParser docs

[mwinterde]

Resolve error in StructuredOutputParser docs

Documentation for StructuredOutputParser currently not reproducible, that is, output_parser.parse(output) raises an error because the LLM returns a response with an invalid format

_input = prompt.format_prompt(question="what's the capital of france")
output = model(_input.to_string())

output

# ?
#
# ```json
# {
# 	"answer": "Paris",
# 	"source": "https://www.worldatlas.com/articles/what-is-the-capital-of-france.html"
# }
# ```

Was fixed by adding a question mark to the prompt

[eyurtsev]

@mwinterde it's possible that this is variation from the underlying llm as well.

[hwchase17]

thanks!