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/ir_qweb.py
if 'async' in kw:
            async_load = kw['async']
        files, remains = self._get_asset_content(xmlid, options)
        asset = self.get_asset_bundle(xmlid, files, env=self.env)
        remains = [node for node in remains if (css and node[0] == 'link') or (js and node[0] != 'link')]
        return remains + asset.to_node(css=css, js=js, debug=debug, async_load=async_load)
    @tools.ormcache_context('xmlid', 'options.get("lang", "en_US")', keys=("website_id",))
    def _get_asset_content(self, xmlid, options):
        options = dict(options,
            inherit_branding=False, inherit_branding_auto=False,
            edit_translations=False, translatable=False,
            rendering_bundle=True)
        env = self.env(context=options)
        def can_aggregate(url):