Add getUri signature to TypeScript definition. (#1736)

* Add `getUri` signature to TypeScript definition.

This is in support of #1624.

* Make configuration optional.

index.d.ts

@@ -128,6 +128,7 @@ export interface AxiosInstance {
     request: AxiosInterceptorManager<AxiosRequestConfig>;
     response: AxiosInterceptorManager<AxiosResponse>;
   };
+  getUri(config?: AxiosRequestConfig): string;
   request<T = any, R = AxiosResponse<T>> (config: AxiosRequestConfig): Promise<R>;
   get<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig): Promise<R>;
   delete<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig): Promise<R>;