Upgrade requests to 2.3.0
Merge pull request #1821 from dstufft/upgrade-requests-1.5.X

Upgrade requests to 2.3.0
Bump version
bump changelog
Merge branch '1.5.X'

Conflicts:
	CHANGES.txt
Merge branch 'master' into develop

Conflicts:
	CHANGES.txt
	pip/__init__.py
	pip/_vendor/vendor.txt