do not install requirements.txt on travis at all

Author: gronke

Makefile

@@ -12,7 +12,7 @@ install-dev: deps
 	pip3.6 install flake8-mutable flake8-builtins flake8-mypy bandit bandit-high-entropy-string
 	pip3.6 install -e .
 install-travis:
-	pip3.6 install -Ur requirements.txt -c .travis/constraints.txt
+	pip3.6 install flake8-mutable flake8-builtins flake8-mypy bandit bandit-high-entropy-string
 uninstall:
 	pip3.6 uninstall -y iocage
 check: