check ufmt before flake8 in ci (#1089)

Summary:
`ufmt` (`black + usort`) overlaps with many rules of `flake8`.
`ufmt` can automatically fix many violations given by `flake8`. So we should screen if any errors can be auto fixed by `ufmt` at first to avoid wasting people's time. And only show the rest `flake8` errors that require manual fixes.

Pull Request resolved: #1089

Reviewed By: cyrjano

Differential Revision: D42006058

Pulled By: aobo-y

fbshipit-source-id: 711065a35da4816c7fd30068b1c5734de961caa1

Author: aobo-y

.circleci/config.yml

@@ -141,8 +141,8 @@ jobs:
     steps:
       - checkout
       - pip_install
-      - lint_flake8
       - ufmt_check
+      - lint_flake8
       - sphinx
 
   test_py36_pip: