random port for websocket on dev - HMR

[r3stm4n]

Bug report

running command vuepress dev --port 23300 --host myhost.com docs
should:
listen on 23300 - http
listen on 23301 - HMR (according to https://github.com/vuejs/vuepress/blob/master/lib/dev.js#L105)

but HMR port is random (every run)

Version

0.10.1

Steps to reproduce

run command vuepress dev --port 23300 --host myhost.com docs

What is expected?

port + 1 or provided by options
(according to https://github.com/vuejs/vuepress/blob/master/lib/dev.js#L105)

What is actually happening?

random port for HMR

Other relevant information

• Your OS: Centos7 (server) Linux Mint 18 (client) (on local Mint same problem)
• Node.js version: v8.11.2
• Browser version: Firefox 60.0.1
• Is this a global or local install? Local
• Which package manager did you use for the install? yarn v1.6.0