Use vim-testbed to run Vader tests on Travis

Makefile

@@ -0,0 +1,14 @@
+IMAGE ?= w0rp/ale
+DOCKER = docker run -a stderr --rm -v $(PWD):/testplugin -v $(PWD)/test:/home "$(IMAGE)"
+
+test-setup:
+	docker images -q $(IMAGE) || docker pull $(IMAGE)
+
+test: test-setup
+	vims=$$(docker run --rm $(IMAGE) ls /vim-build/bin | grep -E '^n?vim'); \
+	if [ -z "$$vims" ]; then echo "No Vims found!"; exit 1; fi; \
+	for vim in $$vims; do \
+	  $(DOCKER) $$vim '+Vader! test/*'; \
+	done
+
+.PHONY: test-setup test