Remove lint from travis-script target.

This means that we will not run lint checks for every build
combination but instead lean on the single lint build in Travis
that runs against the latest version of Python.

Makefile

@@ -29,7 +29,7 @@ travis-install: codeclimate-install  ## Install dependencies for travis-ci.org i
 	@pip install -q -r requirements/travis.txt
 
 .PHONY: travis-script
-travis-script: travis-install tox lint safety-check  ## Entry point for travis-ci.org execution.
+travis-script: travis-install tox safety-check  ## Entry point for travis-ci.org execution.
 
 .PHONY: codeclimate-install
 codeclimate-install:  ## Install dependencies required for codeclimate.com integration.