fix: engine.io-client transport _port handle error

[502647092]

The kind of change this PR does introduce

• [x] a bug fix
• [ ] a new feature
• [ ] an update to the documentation
• [ ] a code change that improves performance
• [ ] other

Current behavior

when port is "443" and this.opts.secure will return ":443"

New behavior

when port is "443" and this.opts.secure will return ""

Other information (e.g. related issues)