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
try:
            content = super(StylesheetAsset, self)._fetch_content()
            web_dir = os.path.dirname(self.url)
            if self.rx_import:
                content = self.rx_import.sub(
                    r"""@import \1%s/""" % (web_dir,),
                    content,
                )
            if self.rx_url:
                content = self.rx_url.sub(
                    r"url(\1%s/" % (web_dir,),
                    content,
                )
            if self.rx_charset:
                
                content = self.rx_charset.sub('', content)
            return content
        except AssetError as e:
            self.bundle.css_errors.append(str(e))
            return ''
    def minify(self):
        
        content = self.rx_sourceMap.sub('', self.content)
        
        content = re.sub(r'/\*.*?\*/', '', content, flags=re.S)
        
        content = re.sub(r'\s+', ' ', content)
        content = re.sub(r' *([{}]) *', r'\1', content)
        return self.with_header(content)
    def to_node(self):