chore: fix test for node 6

Author: SimenB

e2e/__tests__/__snapshots__/customMatcherStackTrace.test.js.snap

@@ -9,14 +9,14 @@ FAIL __tests__/asynchronous.test.js
     We expect the stack trace and code fence for this matcher to be shown in the console.
 
        9 | 
-      10 | test('showing the stack trace for an async matcher', async () => {
-    > 11 |   await expect(true).toThrowCustomAsyncMatcherError();
-         |                      ^
-      12 | });
-      13 | 
-      14 | async function toThrowCustomAsyncMatcherError() {
-
-      at Object.toThrowCustomAsyncMatcherError (__tests__/asynchronous.test.js:11:22)
+      10 | test('showing the stack trace for an async matcher', () =>
+    > 11 |   expect(true).toThrowCustomAsyncMatcherError());
+         |                ^
+      12 | 
+      13 | function toThrowCustomAsyncMatcherError() {
+      14 |   const message = () =>
+
+      at Object.toThrowCustomAsyncMatcherError (__tests__/asynchronous.test.js:11:16)
 `;
 
 exports[`works with custom matchers 1`] = `

e2e/custom-matcher-stack-trace/__tests__/asynchronous.test.js

@@ -7,12 +7,11 @@
 
 expect.extend({toThrowCustomAsyncMatcherError});
 
-test('showing the stack trace for an async matcher', async () => {
-  await expect(true).toThrowCustomAsyncMatcherError();
-});
+test('showing the stack trace for an async matcher', () =>
+  expect(true).toThrowCustomAsyncMatcherError());
 
-async function toThrowCustomAsyncMatcherError() {
+function toThrowCustomAsyncMatcherError() {
   const message = () =>
     'We expect the stack trace and code fence for this matcher to be shown in the console.';
-  return {message, pass: false};
+  return Promise.resolve({message, pass: false});
 }