AWS.Response.nextPage(): Don't require callback (#2580)

AWS.Response.nextPage() does not require a callback argument, so make Typescript definition for callback optional.

.changes/next-release/bugfix-Request-aff176f8.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "Request",
+  "description": "Fix nextPage() method signature"
+}

lib/response.d.ts

@@ -8,7 +8,7 @@ export class Response<D, E> {
 		/**
 		 * Creates a new request for the next page of response data, calling the callback with the page data if a callback is provided.
 		 */
-		nextPage(callback: (err: E, data: D) => void): Request<D, E>|void;
+		nextPage(callback?: (err: E, data: D) => void): Request<D, E>|void;
 		/**
 		 * The de-serialized response data from the service.
 		 * Can be null if an error occurred.
@@ -35,4 +35,4 @@ export class Response<D, E> {
 		 * The raw HTTP response object containing the response headers and body information from the server.
 		 */
 		httpResponse: HttpResponse;
-	}
+	}

package.json

@@ -143,4 +143,4 @@
     "helper-test": "mocha scripts/lib/test-helper.spec.js",
     "csm-functional-test": "mocha test/publisher/functional_test"
   }
-}
+}