[TypeScript] fix Property 'then' does not exist on type 'AxiosInstance'.

[k1r0s]

Using typescript. Creating an AxiosInstance with axios::create(...) the returned object cannot be used like this:

import axios from "axios";

const axiosInstance = axios.create({
  baseURL: 'whatever.api',
  timeout: 1000,
  headers: {
    "Content-Type": "application/x-www-form-urlencoded"
    "stuff"..
  },
  withCredentials: true
});

axiosInstance({
   method: "post",
   url: "/resource"
}).then(res => console.log(res.data))
// err 

In javascript this is working perfectly but in typescript you get an error because of wrong typings.

Typings specify that you can do AxiosInstance.get().then or AxiosInstance.put().then but doesn't allow you to do the same as with AxiosStatic and this isn't correct.

The error from TypeScript:
Cannot invoke an expression whose type lacks a call signature. Type 'AxiosInstance' has no compatible call signatures.

My fix properly sets function signatures to axiosInstance and then axiosstatic will extend those signatures as expected.

Its sad that almost nobody uses typescript :(

Any comments appreciated

[nickuraltsev]

Closing in favor of #1192. Thank you for the PR!