Support for Axios >= 0.23 & Typescript with common headers

[Glandos]

Describe the bug
Since Axios 0.23 and the inclusion of axios/axios#4140 types have changed for global headers.

It is now forbidden to set axios.defaults.headers.Authorization = 'Bearer {auth_token}' and it must be set in axios.defaults.headers.common instead.

However vue-auth-plugin skip non-strings value in

vue-auth-plugin/src/lib/auth-vue-http.ts

Line 173 in fda160e

&& this.options.headerTokenReplace

Header is not replaced, and authenticated requests failed.

Expected behavior
Header should be replaced.

Additional context
Maybe the test should go deeper to handle common, get, post, etc, headers.