Fix test execution errors specific to python3.6

Makefile

@@ -5,6 +5,7 @@ VIRTUAL_ENV ?= $(WORKON_HOME)/pymodbus
 PATH := $(VIRTUAL_ENV)/bin:$(PATH)
 MAKE := $(MAKE) --no-print-directory
 SHELL = bash
+PYVER=$(shell python -c "import sys;t='{v[0]}.{v[1]}'.format(v=list(sys.version_info[:2]));print(t)")
 
 default:
 	@echo 'Makefile for pymodbus'
@@ -37,10 +38,16 @@ check: install
 	@pip install --upgrade --quiet --requirement=requirements-checks.txt
 	@flake8
 
+
 test: install
 	@pip install --upgrade --quiet --requirement=requirements-tests.txt
+ifeq ($(PYVER),3.6)
 	@pytest --cov=pymodbus/ --cov-report term-missing  test/test_server_asyncio.py test
 	@coverage report --fail-under=90 -i
+else
+	@pytest --cov=pymodbus/ --cov-report term-missing
+	@coverage report --fail-under=90 -i
+endif
 
 tox: install
 	@pip install --upgrade --quiet tox && tox
@@ -57,6 +64,7 @@ publish: install
 	twine upload dist/*
 	$(MAKE) clean
 
+
 clean:
 	@rm -Rf *.egg .eggs *.egg-info *.db .cache .coverage .tox build dist docs/build htmlcov doc/_build test/.Python test/pip-selfcheck.json test/lib/ test/include/ test/bin/
 	@find . -depth -type d -name __pycache__ -exec rm -Rf {} \;