fix(types): extend Axios.AxiosRequestConfig with "progress" option (#408)

As documented in https://axios.nuxtjs.org/options.html#progress, Nuxt Axios
supports passing "progress" boolean through request options.

Author: rchl

Diff for: types/index.d.ts

@@ -29,7 +29,7 @@ interface AxiosOptions {
   browserBaseURL?: string,
   credentials?: boolean,
   debug?: boolean,
-  host?: string,     
+  host?: string,
   prefix?: string,
   progress?: boolean,
   proxyHeaders?: boolean,
@@ -49,6 +49,12 @@ interface AxiosOptions {
   },
 }
 
+declare module 'axios' {
+    interface AxiosRequestConfig {
+        progress?: boolean;
+    }
+}
+
 declare module '@nuxt/vue-app' {
   interface Context {
     $axios: NuxtAxiosInstance