The current base image for Python3.6 has pip 9.0.1, which is 2+ years old. I noticed this when I tried to get rid of dependency_links in the setup.py of my package. Can we update pip to 18+ version?
context about dependency_links:
This PR fixed the dependency_links issue:
Try forcing a new version with python: 3.6.7 or using a Xenial image (dist: xenial and python: '3.6'). python: 3.6 on Trusty will always point to an older version of Python, preferring to use the pre-installed version of Python 3.6.x on the image to save time.
https://travis-ci.org/BanzaiMan/travis_production_test/jobs/470178355#L438