[pypy-dev] pip_pypy3 throws exception when updating

[Joseph Reagle]

Homebrew on MacOS Mojave just updated to pypy3 7.0.0 and reminded me to update the setup tools. Doing so, though, throws an exceptions.


```
─➤  pip_pypy3 install --upgrade pip setuptools
Collecting pip
  Using cached https://files.pythonhosted.org/packages/d7/41/34dd96bd33958e52cb4da2f1bf0818e396514fd4f4725a79199564cd0c20/pip-19.0.2-py2.py3-none-any.whl
Collecting setuptools
  Using cached https://files.pythonhosted.org/packages/d1/6a/4b2fcefd2ea0868810e92d519dacac1ddc64a2e53ba9e3422c3b62b378a6/setuptools-40.8.0-py2.py3-none-any.whl
Installing collected packages: pip, setuptools
  Found existing installation: pip 10.0.1
    Uninstalling pip-10.0.1:
      Successfully uninstalled pip-10.0.1
  Found existing installation: setuptools 39.0.1
    Uninstalling setuptools-39.0.1:
      Successfully uninstalled setuptools-39.0.1
Successfully installed pip-19.0.2 setuptools-40.8.0
Traceback (most recent call last):
  File "/usr/local/bin/pip_pypy3", line 11, in <module>
    sys.exit(main())
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/__init__.py", line 246, in main
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/basecommand.py", line 264, in main
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/basecommand.py", line 81, in _build_session
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/download.py", line 338, in __init__
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/download.py", line 127, in user_agent
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_internal/utils/misc.py", line 829, in get_installed_version
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 558, in __init__
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 614, in add_entry
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 1882, in find_eggs_in_zip
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 1399, in has_metadata
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 1756, in _has
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 1633, in zipinfo
  File "/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/pip-10.0.1-py3.6.egg/pip/_vendor/pkg_resources/__init__.py", line 1590, in load
FileNotFoundError: [Errno 2] No such file or directory: '/usr/local/Cellar/pypy3/7.0.0/libexec/site-packages/setuptools-39.0.1-py3.6.egg'
╭─reagle at hom ~
╰─➤  pip_pypy3 install --upgrade pip setuptools                                               1 ↵
Requirement already up-to-date: pip in /usr/local/Cellar/pypy3/7.0.0/libexec/site-packages (19.0.2)
Requirement already up-to-date: setuptools in /usr/local/Cellar/pypy3/7.0.0/libexec/site-packages (40.8.0)
╭─reagle at hom ~
╰─➤
```