cert_pb2.py requires an update

[liaralabs]

Hey there, excellent project and thanks for your work.

Thought you might be interested in knowing that protobuf recently updated to 4.21 in python which renders the current cert_pb2.py invalid for use with 4.21 and will cause errors for anyone attempting to build the project as of about last week or so.

Working solutions are to either:

• pin protobuf to <4 via requirements.txt
• regenerate the protocol buffers with a newer version of protoc