Bump attrs from 19.1.0 to 19.3.0 in /requirements (#5544)

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.1.0 to 19.3.0.
- [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/19.1.0...19.3.0)

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

requirements/common.txt

@@ -368,9 +368,9 @@ first==2.0.2 \
     --hash=sha256:ff285b08c55f8c97ce4ea7012743af2495c9f1291785f163722bd36f6af6d3bf
 
 # Required by jsonschema
-attrs==19.1.0 \
-    --hash=sha256:69c0dbf2ed392de1cb5ec704444b08a5ef81680a61cb899dc08127123af36a79 \
-    --hash=sha256:f0b870f674851ecbfbbbd364d6b5cbdff9dcedbc7f3f5e18a6891057f21fe399
+attrs==19.3.0 \
+    --hash=sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c \
+    --hash=sha256:f7b7ce16570fe9965acd6d30101a28f62fb4a7f9e926b3bbc9b61f8b04247e72
 pyrsistent==0.15.4 \
     --hash=sha256:34b47fa169d6006b32e99d4b3c4031f155e6e68ebcc107d6454852e8e0ee6533