Update all pypi.python.org URLs to pypi.org

For details on the new PyPI, see the blog post:

https://pythoninsider.blogspot.ca/2018/04/new-pypi-launched-legacy-pypi-shutting.html

doc/en/getting-started.rst

@@ -5,10 +5,10 @@ Installation and Getting Started
 
 **Platforms**: Unix/Posix and Windows
 
-**PyPI package name**: `pytest <http://pypi.python.org/pypi/pytest>`_
+**PyPI package name**: `pytest <https://pypi.org/project/pytest/>`_
 
-**Dependencies**: `py <http://pypi.python.org/pypi/py>`_,
-`colorama (Windows) <http://pypi.python.org/pypi/colorama>`_,
+**Dependencies**: `py <https://pypi.org/project/py/>`_,
+`colorama (Windows) <https://pypi.org/project/colorama/>`_,
 
 **Documentation as PDF**: `download latest <https://media.readthedocs.org/pdf/pytest/latest/pytest.pdf>`_