old_contents: from readme_renderer.rst import render
  
  
  def test_markup_is_generated():
      with open('README.rst') as f:
          assert render(f.read()) is not None
  
new_contents: try:
      from io import StringIO  # python3
  except ImportError:
      from cStringIO import StringIO  # python2
  from readme_renderer.rst import render
  
  
  def test_markup_is_generated():
      warnings = StringIO()
      with open('README.rst') as f:
          html = render(f.read(), stream=warnings)
          warnings.seek(0)
          assert html is not None, warnings.read()
  
subject: update readme test