error in Downloading the example OPA

Hi, 
First of all, thank you for your contribution :). I have an issue while using the "Sudo pip install -r requirements.txt"; which is rejected by pip.

Invalid requirement: 'networkx=2.2'
= is not a valid operator. Did you mean == ?

I tried to fix the text file by replacing == instead of =, but nothing changed. 

Regards,
Sara
