Invalid "heartbeat interval" option when using engine.io@^4.0.0

[chris-allen]

In attempting to comply with CVE-2020-36048, forcing engine.io to resolve to ^4.0.0 results in the following error:

Option heartbeat interval is not valid. Please refer to the README.

I don't see the removal of the heartbeat interval option called out in the enginge.io CHANGELOG, but there is this blog post about the engine.io 4 release (now on 6.1.2).

Browsersync	Node	Npm
2.27.7	4.18.3	6.14.15

Usage

gulp.task('watch', function() {
  browserSync.init({
    socket: {
      domain: 'myapp-sync.lndo.site'
    },
    logLevel: 'silent',
    notify: false,
    cors: true,
    server: {
      baseDir: '.',
    },
    open: false,
  });
  ...
});

[lachieh]

Duplicate issue. See #1850 for original.