Networkx package missing from the requirements

[DanelArias-Dreyton257]

Installing qiskit-ibm-transpiler for 0.11.0 does not install networkx which is necessary imported in ai_local_synthesis.py.
I think adding this to the setup.py might be an easy fix.

In my case, using the same version as the one defined in requirements-dev.txt worked just fine.

[jesus-talavera-ibm]

Thank you @DanelArias-Dreyton257 ! We've prepared the fix in #172