[Bug report] - PyQt5 pip version-finding issue in iblenv requirements installation

[chris-langfield]

Describe the bug
When installing from the requirements.txt file in iblenv, pip cannot find a compatible PyQt5 version.
To Reproduce
Following steps in https://github.com/int-brain-lab/iblenv#install-from-scratch for clean install. After using the workaround in #335 to get past the PyQt5 hanging problem, the following line causes this error:

pip install --requirement requirements.txt

The message:

Collecting pyopengl
  Using cached PyOpenGL-3.1.6-py3-none-any.whl (2.4 MB)
ERROR: Ignored the following versions that require a different python version: 0.7 Requires-Python >=3.6, <3.7; 0.8 Requires-Python >=3.6, <3.7
ERROR: Could not find a version that satisfies the requirement PyQt5==5.12.3 (from versions: 5.14.0, 5.14.1, 5.14.2, 5.15.0, 5.15.1, 5.15.2, 5.15.3, 5.15.4, 5.15.5, 5.15.6, 5.15.7, 5.15.8, 5.15.9)
ERROR: No matching distribution found for PyQt5==5.12.3

[chris-langfield]

Removing the version lock for non-Windows systems as suggested in this version of the README seems to work, but is that lock still important/needed?

6171812

[bimac]

without having tested this myself - locking PyQt5 to a specific version doesn't sound like a great idea to me

[bimac]

#327

[k1o0]

See #327