Forcing pyzmq version for conda

[anpaz]

We know iqsharp has problems with newer versions of pyzmq, however the version is not locked for conda which presumably is causing the timeouts we see on our e2e builds.

[cgranade]

@anpaz: I think I finally nailed down why this is failing to build. It looks like PyZMQ versions before 20.0 aren't compatible with Python 3.9 and later:

➜  conda create -n py39-zmq python=3.9 pyzmq<20 
Collecting package metadata (current_repodata.json): done
Solving environment: failed with repodata from current_repodata.json, will retry with next repodata source.
Collecting package metadata (repodata.json): done
Solving environment: - 
Found conflicts! Looking for incompatible packages.
This can take several minutes.  Press CTRL-C to abort.
                                                                                                                                                                                                                                                                                -
failed

UnsatisfiableError: The following specifications were found to be incompatible with each other:

Output in format: Requested package -> Available versions

Package python conflicts for:
python=3.9
pyzmq[version='<20'] -> python[version='>=2.7,<2.8.0a0|>=3.6,<3.7.0a0|>=3.7,<3.8.0a0|>=3.8,<3.9.0a0|>=3.5,<3.6.0a0']

[anpaz]

This was fixed by updated NetMQ on jupyter-core.