Update deployment.md

[aljones15]

just got it working on Heroku a moment ago

[mathieutu]

Hi, thank you for this work !
However, I think the express part will not work with vue-router.

Also, I'm working on a vue-cli plugin that will permit to do that in a click: mathieutu/vue-cli-plugin-express.
I'll let you know when it'll be usable, and we can integrate it to the doc.

[mathieutu]

For record, duplicate of #2533

[aljones15]

I like the other person's docs look better (and they already implemented vue router so closing this)