Bump fsspec[s3] from 2021.08.1 to 2021.9.0 (#838)

Bumps [fsspec[s3]](https://github.com/intake/filesystem_spec) from 2021.08.1 to 2021.9.0.
- [Release notes](https://github.com/intake/filesystem_spec/releases)
- [Commits](fsspec/filesystem_spec@2021.08.1...2021.09.0)

---
updated-dependencies:
- dependency-name: fsspec[s3]
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev_optional.txt

@@ -18,5 +18,5 @@ flake8==3.9.2
 pytest-cov==2.12.1
 pytest-doctestplus==0.11.0
 h5py==3.4.0
-fsspec[s3]==2021.08.1
+fsspec[s3]==2021.9.0
 moto[server]>=1.3.14