Head function from nuxt.config.js is only considered on the first request

[TheAlexLichter]

Hey 👋🏻

First of all, sorry for the long title 🙈

When defining a head function or object in the nuxt.config.js, it is only evaluated and taken into consideration on the first request / first page a user is visiting.

Reproduction: https://codesandbox.io/s/codesandboxnuxt-oqqsj

Steps:

1. Go to https://oqqsj.sse.codesandbox.io/
2. Open inspector -> see tabindex="0" on the body
3. Click the link to go to /about (it has to be the link, no manual input).
4. tabindex="0" is gone.

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Originally reported by @codeofsumit

[pimlie]

The issue seems to be that 0 is a falsy value, if I use tabIndex: 1 it keeps being listed. Working on a fix.