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.
from __future__ import print_function
import ast
import json
import logging
from collections import OrderedDict
from time import time
from lxml import html
from lxml import etree
from werkzeug import urls
from odoo.tools import pycompat
from odoo import api, models, tools
from odoo.tools.safe_eval import assert_valid_codeobj, _BUILTINS, _SAFE_OPCODES
from odoo.http import request
from odoo.modules.module import get_resource_path
from .qweb import QWeb, Contextifier
from .assetsbundle import AssetsBundle
_logger = logging.getLogger(__name__)
class IrQWeb(models.AbstractModel, QWeb):
    """ Base QWeb rendering engine
    * to customize ``t-field`` rendering, subclass ``ir.qweb.field`` and
      create new models called :samp:`ir.qweb.field.{widget}`
    Beware that if you need extensions or alterations which could be
    incompatible with other subsystems, you should create a local object
    inheriting from ``ir.qweb`` and customize that.
    """
    _name = 'ir.qweb'
    @api.model
    def render(self, id_or_xml_id, values=None, **options):