Stick with pip for travis testing

Makefile

@@ -55,7 +55,7 @@ dev/%: ## run a foreground container for a stack
 	docker run -it --rm -p $(PORT):8888 $(DARGS) $(OWNER)/$(notdir $@) $(ARGS)
 
 dev-env: ## install libraries required to build docs and run tests
-	conda env create -f environment.yml
+	pip install -r requirements-dev.txt
 
 docs: ## build HTML documentation
 	make -C docs html

environment.yml

-name: docker-stacks
-channels:
-  - conda-forge
-dependencies:
-- python=3.6
-- pytest
-- requests
-- sphinx>=1.6
-- sphinx_rtd_theme
-- pip:
-  - docker
-  - jupyter_alabaster_theme
-  - recommonmark==0.4.0
\ No newline at end of file

requirements-dev.txt

+docker
+jupyter_alabaster_theme
+pytest
+recommonmark==0.4.0
+requests
+sphinx>=1.6
+sphinx_rtd_theme
\ No newline at end of file