Replace use of dict.has_key with `key in dict`

    linenos = node.rawsource.count('\n') >= self.highlightlinenothreshold - 1

    fname = node['filename']

    highlight_args = node.get('highlight_args', {})

    if node.has_key('language'):

    if 'language' in node:

        # code-block directives

        lang = node['language']

        highlight_args['force'] = True

    if node.has_key('linenos'):

    if 'linenos' in node:

        linenos = node['linenos']

    def warner(msg):