Replace broken link

Diveintopython.net is no longer available. Replacing it for another mirror of the book.

Author: igorrocha

example-data-science-notebook/Example Machine Learning Notebook.ipynb

@@ -2296,7 +2296,7 @@
  "\n",
  "**Machine Learning**: /r/MachineLearning has a useful [Wiki page](https://www.reddit.com/r/MachineLearning/wiki/index) containing links to online courses, books, data sets, etc. for Machine Learning. There's also a [curated list](https://github.com/josephmisiti/awesome-machine-learning) of Machine Learning frameworks, libraries, and software sorted by language.\n",
  "\n",
- "**Unit testing**: Dive Into Python 3 has a [great walkthrough](http://www.diveintopython3.net/unit-testing.html) of unit testing in Python, how it works, and how it should be used\n",
+ "**Unit testing**: Dive Into Python 3 has a [great walkthrough](https://www.diveinto.org/python3/unit-testing.html) of unit testing in Python, how it works, and how it should be used\n",
  "\n",
  "**pandas** has [several tutorials](http://pandas.pydata.org/pandas-docs/stable/tutorials.html) covering its myriad features.\n",
  "\n",