filterUpgrades(upgrades) {
        const filteredUpgrades = [];
        let i = 0;
        const j = upgrades.length;
        for (; i < j; i++) {
            if (~this.transports.indexOf(upgrades[i]))
                filteredUpgrades.push(upgrades[i]);
        }
        return filteredUpgrades;
    }
Filters upgrades, returning only those matching client transports.

@param {Array} server upgrades
@api private