Silence some flake8 errors

Summary:
I find some flake8 errors very annoying, particularly those about hanging indent. This code triggers a flake8 error:
```
very_long_function_name(
      param1, param2, param3)
```
While this one does not:
```
very_long_function_(
param1, param2, param3)
```

I personally find the former way more readable. This diff disables this warning.

Test Plan: Manual tests.

Reviewers: emfree, kav-ya

Reviewed By: kav-ya

Differential Revision: https://review.inboxapp.com/D759