Fix 'install_requires' to include semver

[maretodoric]

When installing version 4.0.1 on freshly configured python virtual environment, and when attempting to import bullmq module, I've noticed error message:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/mtodoric/dev-in-progress/fapi_esalertmanager/esam_test/lib/python3.10/site-packages/bullmq/__init__.py", line 10, in <module>
    from bullmq.queue import Queue
  File "/home/mtodoric/dev-in-progress/fapi_esalertmanager/esam_test/lib/python3.10/site-packages/bullmq/queue.py", line 3, in <module>
    from bullmq.scripts import Scripts
  File "/home/mtodoric/dev-in-progress/fapi_esalertmanager/esam_test/lib/python3.10/site-packages/bullmq/scripts.py", line 9, in <module>
    from bullmq.utils import isRedisVersionLowerThan
  File "/home/mtodoric/dev-in-progress/fapi_esalertmanager/esam_test/lib/python3.10/site-packages/bullmq/utils.py", line 1, in <module>
    import semver
ModuleNotFoundError: No module named 'semver'

This PR should include semver as dependeny and fix this issue.
requirements.txt already seems to be updated.

[roggervalf]

Lgtm