Remove outdated warning about Python version mixing with Pipenv (pypa#501)

Resolves pypa#452

Author: theacodes

source/tutorials/managing-dependencies.rst

@@ -113,16 +113,7 @@ when you share your project with others. You should get output similar to this
     Adding requests to Pipfile's [packages]...
     P.S. You have excellent taste! ✨ 🍰 ✨
 
-.. Warning:: Due to an `open issue with pipenv`_, it's not currently reliable
-    to use ``pipenv`` to create environments for different Python versions
-    (as environment marker conditions may not be processed correctly).
-    The interpreter version you use in your project should be the same as the
-    interpreter version used to install ``pipenv``.
-    When testing against multiple versions with ``tox``, install ``pipenv``
-    into each test environment, as described `here <pipenv-tox>`_.
-
 .. _Requests: https://python-requests.org
-.. _open issue with pipenv: https://github.com/pypa/pipenv/issues/857
 .. _pipenv-tox: https://docs.pipenv.org/advanced/#tox-automation-project