update README linter

Author: mr-c

setup.py

@@ -23,6 +23,7 @@
       version='1.0',
       description='Common workflow language reference implementation',
       long_description=open(README).read(),
+      long_description_content_type="text/x-rst",
       author='Common workflow language working group',
       author_email='[email protected]',
       url="https://github.com/common-workflow-language/cwltool",

tox.ini

@@ -61,9 +61,14 @@ deps =
   pip==9.0.3
 
 [testenv:py27-lint-readme]
-commands = python setup.py check -r -s
+commands =
+  python setup.py sdist
+  python setup.py bdist_wheel
+  twine check dist/*
 deps =
-    readme
+    twine
+    wheel
+    readme_renderer[md]
 
 [testenv:py27-pydocstyle]
 whitelist_externals = make