qa: add flake8 to check make target

.travis.yml

@@ -12,4 +12,4 @@ install:
     fi
 script:
   - vim --version
-  - make "$ENV"
+  - make --keep-going "$ENV"

Makefile

@@ -1,16 +1,26 @@
 test:
-	py.test
+	pytest test_*.py
 
 build:
 	mkdir $@
+
 build/vint: | build
 	virtualenv -p python3.6 $@
 	$@/bin/pip install vim-vint==0.3.19
-check: LINT_FILES:=after autoload ftplugin plugin
-check: build/vint
-	build/vint/bin/vint $(LINT_FILES)
+
+build/flake8: | build
+	virtualenv -p python3.6 $@
+	$@/bin/pip install flake8==3.5.0
+
+vint: build/vint
+	build/vint/bin/vint after autoload ftplugin plugin
+
+flake8: build/flake8
+	build/flake8/bin/flake8 pythonx/jedi_*.py
+
+check: vint flake8
 
 clean:
 	rm -rf build
 
-.PHONY: test check clean
+.PHONY: test check clean vint flake8