add a stack in summary

I want to add a stack in summary, since it's often hard to identify which expect it failed.

Such as the following:
```
expect(booleanA).toBe(expectedA)
expect(booleanB).toBe(expectedB)
expect(booleanC).toBe(expectedC)
```
This failure message will be
```
Expected true to be false.
```
I couldn't tell which except is failed only by looking at the message.
In this situation, I usually rerun the test on a browser, because the summary shows stacks like I added in this pull request.