Invoke on_error_handler as described in the docs

[dlenskiSB]

According to the example in the README, the on_error handler should be called with two parameters, of which the first is the CertStreamClient instance:

https://github.com/CaliDog/certstream-python/blob/97eb5b37e2c2077495e20d6df3459088a5262b48/README.md?plain=1#L61-L63