Update vendor packaging in pkg_resources to v19.2

[ozars]

Summary of changes

I bumped the version of vendor packaging of pkg_resources to v19.2 using the script proposed in #2179. I bumped it to v19.2 to keep it consistent with the version of packaging vendored under setuptools, but I can update this vendor to the latest version along with others as well if that's okay?

Closes #2175.

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d. See documentation for details

[jaraco]

In c30aca8, I ran pip-run paver -- -m paver update_vendored and it produced a small diff:

diff --git a/pkg_resources/_vendor/packaging/requirements.py b/pkg_resources/_vendor/packaging/requirements.py
index a175b8a2..c3424dcb 100644
--- a/pkg_resources/_vendor/packaging/requirements.py
+++ b/pkg_resources/_vendor/packaging/requirements.py
@@ -70,7 +70,7 @@ URL_AND_MARKER = URL + Optional(MARKER)
 NAMED_REQUIREMENT = NAME + Optional(EXTRAS) + (URL_AND_MARKER | VERSION_AND_MARKER)
 
 REQUIREMENT = stringStart + NAMED_REQUIREMENT + stringEnd
-# pyparsing isn't thread safe during initialization, so we do it eagerly, see
+# pkg_resources.extern.pyparsing isn't thread safe during initialization, so we do it eagerly, see
 # issue #104
 REQUIREMENT.parseString("x[]")

So I used that for consistency. I've also added a changelog entry.