setup.py: adjust websockets versions for py38-310

According to the websockets changelog[0]:
  - v8.0 requires python >= 3.6
  - v8.1 adds support for python3.8
  - v9.0 adds support for python3.9
  - v10.0 adds support for python3.10

This change is attempting to cover all these scenarios. The previous
behavior was allowing some unwanted scenarios, e.g. websockets==9.0 and
python3.10 combination. Which is incompatible.

[0] https://websockets.readthedocs.io/en/stable/project/changelog.html

Closes #730

Signed-off-by: Mert Kırpıcı <mert.kirpici@canonical.com>

Author: Mert Kırpıcı

setup.py

@@ -36,9 +36,10 @@
         'pyRFC3339>=1.0,<2.0',
         'pyyaml>=5.1.2,<=6.0',
         'theblues>=0.5.1,<1.0',
-        'websockets>=7.0,<8.0 ; python_version<"3.9"',
-        'websockets>=8.0,<9.0 ; python_version=="3.9"',
-        'websockets>=9.0; python_version>"3.9"',
+        'websockets>=7.0,<8.1 ; python_version<"3.8"',
+        'websockets>=8.1,<9.0 ; python_version=="3.8"',
+        'websockets>=9.0,<10.0 ; python_version=="3.9"',
+        'websockets>=10.0; python_version>"3.9"',
         'paramiko>=2.4.0,<3.0.0',
         'pyasn1>=0.4.4',
         'toposort>=1.5,<2',