Bump attrs from 19.3.0 to 20.1.0 in /requirements (#15343)

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.3.0 to 20.1.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/python-attrs/attrs/compare/19.3.0...20.1.0)

Signed-off-by: dependabot[bot] <support@github.com>

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

requirements/tests.txt

@@ -68,9 +68,9 @@ argh==0.26.2 \
     --hash=sha256:e9535b8c84dc9571a48999094fda7f33e63c3f1b74f3e5f3ac0105a58405bb65
 pathtools==0.1.2 \
     --hash=sha256:7c35c5421a39bb82e58018febd90e3b6e5db34c5443aaaf742b3f33d4655f1c0
-attrs==19.3.0 \
-    --hash=sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c \
-    --hash=sha256:f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72
+attrs==20.1.0 \
+    --hash=sha256:2867b7b9f8326499ab5b0e2d12801fa5c98842d2cbd22b35112ae04bf85b4dff \
+    --hash=sha256:0ef97238856430dcf9228e07f316aefc17e8939fc8507e18c6501b761ef1a42a
 pluggy==0.13.1 \
     --hash=sha256:15b2acde666561e1298d71b523007ed7364de07029219b604cf808bfa1c765b0 \
     --hash=sha256:966c145cd83c96502c3c3868f50408687b38434af77734af1e9ca461a4081d2d