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
tagName, attributes, content = self.to_node()
        html = u"<%s " % tagName
        for name, value in attributes.items():
            if value or isinstance(value, string_types):
                html += u' %s="%s"' % (name, escape(to_text(value)))
        if content is None:
            html += u'/>'
        else:
            html += u'>%s</%s>' % (escape(to_text(content)), tagName)
        return html
    def to_node(self):
        raise NotImplementedError()
    @func.lazy_property
    def last_modified(self):
        try:
            self.stat()
            if self._filename:
                return datetime.fromtimestamp(os.path.getmtime(self._filename))
            elif self._ir_attach:
                server_format = tools.DEFAULT_SERVER_DATETIME_FORMAT
                last_update = self._ir_attach['__last_update']
                try:
                    return datetime.strptime(last_update, server_format + '.%f')
                except ValueError:
                    return datetime.strptime(last_update, server_format)
        except Exception:
            pass
        return datetime(1970, 1, 1)
    @property
    def content(self):