Fix broken link in documentation

docs/source/development/pycompat.rst

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 Writing code for Python 2 and 3
 ===============================
 
 .. module:: IPython.utils.py3compat
    :synopsis: Python 2 & 3 compatibility helpers
 
 
 IPython 6 requires Python 3, so our compatibility module
 ``IPython.utils.py3compat`` is deprecated and will be removed in a future
 version. In most cases, we recommend you use the `six module
-<https://pythonhosted.org/six/>`__ to support compatible code. This is widely
+<https://six.readthedocs.io/>`__ to support compatible code. This is widely
 used by other projects, so it is familiar to many developers and thoroughly
 battle-tested.
 
 Our ``py3compat`` module provided some more specific unicode conversions than
 those offered by ``six``. If you want to use these, copy them into your own code
 from IPython 5.x. Do not rely on importing them from IPython, as the module may
 be removed in the future.
 
 .. seealso::
 
    `Porting Python 2 code to Python 3 <https://docs.python.org/3/howto/pyporting.html>`_
      Official information in the Python docs.
 
-   `Python-Modernize <http://python-modernize.readthedocs.io/en/latest/>`_
+   `Python-Modernize <https://python-modernize.readthedocs.io/en/latest/>`_
      A tool which helps make code compatible with Python 3.
 
-   `Python-Future <http://python-future.org/>`_
+   `Python-Future <https://python-future.org/>`_
      Another compatibility tool, which focuses on writing code for Python 3 and
      making it work on Python 2.