Authorization header capitalization

[MichelJonkman]

The setToken method sets the header as "Authorization" but if there is already an authorization header without capital A they can combined in the final request causing errors to occur. In my case this was the cause of Strapi /users/me giving an 401 response.

Nuxt version: 2.15.8
@nuxt/http version: 0.6.4

[MichelJonkman]

The existing authorization header is the result of an nginx reverse proxy with HTTP basic authentication