DOC: Update a link in cookbook.rst
In the pandas Cookbook, the Time Series - Aggregation and plotting time series has an invalid link:
https://nipunbatra.github.io/blog/visualisation/2013/05/01/aggregation-timeseries.html

This link should be:
https://nipunbatra.github.io/blog/posts/2013-05-01-aggregation-timeseries.html

- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Thanks @star1327p 