215: Update pip to 21.0.1 r=duckinator a=pyup-botThis PR updates [pip](https://pypi.org/project/pip) from **20.3.3** to **21.0.1**.<details>  <summary>Changelog</summary>       ### 21.0.1   ```   ===================Bug Fixes---------- commands: debug: Use packaging.version.parse to compare between versions. (`9461 &lt;https://github.com/pypa/pip/issues/9461&gt;`_)- New resolver: Download and prepare a distribution only at the last possible  moment to avoid unnecessary network access when the same version is already  installed locally. (`9516 &lt;https://github.com/pypa/pip/issues/9516&gt;`_)Vendored Libraries------------------- Upgrade packaging to 20.9   ```          ### 21.0   ```   =================Deprecations and Removals-------------------------- Drop support for Python 2. (`6148 &lt;https://github.com/pypa/pip/issues/6148&gt;`_)- Remove support for legacy wheel cache entries that were created with pip  versions older than 20.0. (`7502 &lt;https://github.com/pypa/pip/issues/7502&gt;`_)- Remove support for VCS pseudo URLs editable requirements. It was emitting  deprecation warning since version 20.0. (`7554 &lt;https://github.com/pypa/pip/issues/7554&gt;`_)- Modernise the codebase after Python 2. (`8802 &lt;https://github.com/pypa/pip/issues/8802&gt;`_)- Drop support for Python 3.5. (`9189 &lt;https://github.com/pypa/pip/issues/9189&gt;`_)- Remove the VCS export feature that was used only with editable VCS  requirements and had correctness issues. (`9338 &lt;https://github.com/pypa/pip/issues/9338&gt;`_)Features--------- Add ``--ignore-requires-python`` support to pip download. (`1884 &lt;https://github.com/pypa/pip/issues/1884&gt;`_)- New resolver: Error message shown when a wheel contains inconsistent metadata  is made more helpful by including both values from the file name and internal  metadata. (`9186 &lt;https://github.com/pypa/pip/issues/9186&gt;`_)Bug Fixes---------- Fix a regression that made ``pip wheel`` do a VCS export instead of a VCS clone  for editable requirements. This broke VCS requirements that need the VCS  information to build correctly. (`9273 &lt;https://github.com/pypa/pip/issues/9273&gt;`_)- Fix ``pip download`` of editable VCS requirements that need VCS information  to build correctly. (`9337 &lt;https://github.com/pypa/pip/issues/9337&gt;`_)Vendored Libraries------------------- Upgrade msgpack to 1.0.2.- Upgrade requests to 2.25.1.Improved Documentation----------------------- Render the unreleased pip version change notes on the news page in docs. (`9172 &lt;https://github.com/pypa/pip/issues/9172&gt;`_)- Fix broken email link in docs feedback banners. (`9343 &lt;https://github.com/pypa/pip/issues/9343&gt;`_).. note    You should *NOT* be adding new change log entries to this file, this    file is managed by towncrier. You *may* edit previous change logs to    fix problems like typo corrections or such.    To add a new change log entry, please seehttps://pip.pypa.io/en/latest/development/contributing/#news-entries.. towncrier release notes start   ```          ### 20.3.4   ```   ===================Features--------- ``pip wheel`` now verifies the built wheel contains valid metadata, and can be  installed by a subsequent ``pip install``. This can be disabled with  ``--no-verify``. (`9206 &lt;https://github.com/pypa/pip/issues/9206&gt;`_)- Improve presentation of XMLRPC errors in pip search. (`9315 &lt;https://github.com/pypa/pip/issues/9315&gt;`_)Bug Fixes---------- Fixed hanging VCS subprocess calls when the VCS outputs a large amount of data  on stderr. Restored logging of VCS errors that was inadvertently removed in pip  20.2. (`8876 &lt;https://github.com/pypa/pip/issues/8876&gt;`_)- Fix error when an existing incompatibility is unable to be applied to a backtracked state. (`9180 &lt;https://github.com/pypa/pip/issues/9180&gt;`_)- New resolver: Discard a faulty distribution, instead of quitting outright.  This implementation is taken from 20.2.2, with a fix that always makes the  resolver iterate through candidates from indexes lazily, to avoid downloading  candidates we do not need. (`9203 &lt;https://github.com/pypa/pip/issues/9203&gt;`_)- New resolver: Discard a source distribution if it fails to generate metadata,  instead of quitting outright. This implementation is taken from 20.2.2, with a  fix that always makes the resolver iterate through candidates from indexes  lazily, to avoid downloading candidates we do not need. (`9246 &lt;https://github.com/pypa/pip/issues/9246&gt;`_)Vendored Libraries------------------- Upgrade resolvelib to 0.5.4.   ```     </details> <details>  <summary>Links</summary>    - PyPI:https://pypi.org/project/pip  - Changelog:https://pyup.io/changelogs/pip/  - Homepage:https://pip.pypa.io/</details>Co-authored-by: pyup-bot <github-bot@pyup.io>