Log Message:
py-pip: updated to 19.1

19.1:

Features
- Configuration files may now also be stored under sys.prefix
- Avoid creating an unnecessary local clone of a Bazaar branch when exporting.
- Include in pip's User-Agent string whether it looks like pip is running
  under CI.
- A custom (JSON-encoded) string can now be added to pip's User-Agent
  using the PIP_USER_AGENT_USER_DATA environment variable.
- For consistency, passing --no-cache-dir no longer affects whether wheels
  will be built.  In this case, a temporary directory is used.
- Command arguments in subprocess log messages are now quoted using
  shlex.quote().
- Prefix warning and error messages in log output with WARNING and ERROR.
- Using --build-options in a PEP 517 build now fails with an error,
  rather than silently ignoring the option.
- Error out with an informative message if one tries to install a
  pyproject.toml-style (PEP 517) source tree using --editable mode.
- When downloading a package, the ETA and average speed now only update once per \ 
second for better legibility.

Bug Fixes
- The stdout and stderr from VCS commands run by pip as subprocesses (e.g.
  git, hg, etc.) no longer pollute pip's stdout.
- Fix handling of requests exceptions when dependencies are debundled.
- Make pip's self version check avoid recommending upgrades to prereleases if \ 
the currently-installed version is stable.
- Fixed crash when installing a requirement from a URL that comes from a \ 
dependency without a URL.
- Improve handling of file URIs: correctly handle file://localhost/... and don't \ 
try to use UNC paths on Unix.
- Fix utils.encoding.auto_decode() LookupError with invalid encodings.
  utils.encoding.auto_decode() was broken when decoding Big Endian BOM
  byte-strings on Little Endian or vice versa.
- Fix incorrect URL quoting of IPv6 addresses.
- Redact the password from the extra index URL when using pip -v.
- The spinner no longer displays a completion message after subprocess calls
  not needing a spinner. It also no longer incorrectly reports an error after
  certain subprocess calls to Git that succeeded.
- Fix the handling of editable mode during installs when pyproject.toml is
  present but PEP 517 doesn't require the source tree to be treated as
  pyproject.toml-style.
- Fix NameError when handling an invalid requirement.

Vendored Libraries
- Updated certifi to 2019.3.9
- Updated distro to 1.4.0
- Update progress to 1.5
- Updated pyparsing to 2.4.0
- Updated pkg_resources to 41.0.1 (via setuptools)

Improved Documentation
- Make dashes render correctly when displaying long options like
  --find-links in the text.