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
""" Minify js with a clever regex.
    Taken from http://opensource.perlig.de/rjsmin
    Apache License, Version 2.0 """
    def subber(match):
        """ Substitution callback """
        groups = match.groups()
        return (
            groups[0] or
            groups[1] or
            groups[2] or
            groups[3] or
            (groups[4] and '\n') or
            (groups[5] and ' ') or
            (groups[6] and ' ') or
            (groups[7] and ' ') or
            ''
        )
    result = re.sub(
        r'([^\047"/\000-\040]+)|((?:(?:\047[^\047\\\r\n]*(?:\\(?:[^\r\n]|\r?'
        r'\n|\r)[^\047\\\r\n]*)*\047)|(?:"[^"\\\r\n]*(?:\\(?:[^\r\n]|\r?\n|'
        r'\r)[^"\\\r\n]*)*"))[^\047"/\000-\040]*)|(?:(?<=[(,=:\[!&|?{};\r\n]'