DOC: Insert "pandas" into json_normalize examples
#### Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.json_normalize.html

#### Documentation problem

It seems that in the examples cells the json_normalize is not preceded by pandas. (i.e. pandas dot)
This does not allow to simply copy and paste the examples.

#### Suggested fix for documentation

Just insert " pandas. " preceding the json_normalize() method in the example cells where it is missing.