fix(types): add missing DNS interceptor

nodejs#3684 has backported the DNS interceptor from nodejs#3490. However, the func
that is exported, was not added to TypeScript defs.

Co-authored-by: Carlos Fuentes <[email protected]>

Author: slagiewka

types/interceptors.d.ts

@@ -28,4 +28,5 @@ declare namespace Interceptors {
   export function retry(opts?: RetryInterceptorOpts): Dispatcher.DispatcherComposeInterceptor
   export function redirect(opts?: RedirectInterceptorOpts): Dispatcher.DispatcherComposeInterceptor
   export function responseError(opts?: ResponseErrorInterceptorOpts): Dispatcher.DispatcherComposeInterceptor
+  export function dns (opts?: DNSInterceptorOpts): Dispatcher.DispatcherComposeInterceptor
 }