Battery Status plugin: tests should use console.error() instead of non-existing console.err()

afterEach(function () {
    if (!batteryStatusUnsupported) {
        try {
            window.removeEventListener("batterycritical", onEvent, false);
        }
        catch (e) {
            console.err('Error removing batterycritical event listener: ' + e);
        }
    }
});