getOperationAST: make operationName optional (#2622)

Author: IvanGoncharov

src/utilities/getOperationAST.d.ts

@@ -9,5 +9,5 @@ import { DocumentNode, OperationDefinitionNode } from '../language/ast';
  */
 export function getOperationAST(
   documentAST: DocumentNode,
-  operationName: Maybe<string>,
+  operationName?: Maybe<string>,
 ): Maybe<OperationDefinitionNode>;

src/utilities/getOperationAST.js

@@ -13,7 +13,7 @@ import {
  */
 export function getOperationAST(
   documentAST: DocumentNode,
-  operationName: ?string,
+  operationName?: ?string,
 ): ?OperationDefinitionNode {
   let operation = null;
   for (const definition of documentAST.definitions) {