Writing_Linter_Bears.rst: Fix broken link

This solves the broken link issue Change Dive into python
<http://www.diveintopython3.net/regular-expressions.html>-->
<http://diveintopython3.problemsolving.io/regular-expressions.html>

Closes #5944

docs/Developers/Writing_Linter_Bears.rst

@@ -146,7 +146,7 @@ For the exact list of named groups ``@linter`` recognizes, see the `API
 documentation <https://api.coala.io/en/latest/>`__.
 
 Please refer to `Python3 re module <https://docs.python.org/3/library/re.html>`_
-and `Dive into python <http://www.diveintopython3.net/regular-expressions.html>`_
+and `Dive into python <http://diveintopython3.problemsolving.io/regular-expressions.html>`_
 for information about regular expressions.
 
 Let's brush up our ``output_regex`` a bit to use even more information: