According document of 'What’s New In Python 3.7', 'async' are reserved keywords now.

Code in line 105 of 'odoo/addons/base/ir/ir_qweb/assetsbundle.py' 
`def to_html(self, sep=None, css=True, js=True, debug=False, async=False, url_for=(lambda url: url)):`
will throw SyntaxError out if we launch odoo with this update python.
odoo/addons/base/ir/ir_qweb/assetsbundle.py
if self.url:
            attr = OrderedDict([
                ["type", "text/css"],
                ["rel", "stylesheet"],
                ["href", self.html_url],
                ["media", escape(to_text(self.media)) if self.media else None]
            ])
            return ("link", attr, None)
        else:
            attr = OrderedDict([
                ["type", "text/css"],
                ["media", escape(to_text(self.media)) if self.media else None]
            ])
            return ("style", attr, self.with_header())
class PreprocessedCSS(StylesheetAsset):
    rx_import = None
    def __init__(self, *args, **kw):
        super(PreprocessedCSS, self).__init__(*args, **kw)
        self.html_url_format = '%%s/%s/%%s.css' % self.bundle.name
        self.html_url_args = tuple(self.url.rsplit('/', 1))
    def get_source(self):
        content = self.inline or self._fetch_content()
        return "/*! %s */\n%s" % (self.id, content)
    def get_command(self):
        raise NotImplementedError
class SassStylesheetAsset(PreprocessedCSS):