Allow development events through config

[phoenixbox]

The config parameter of create_client is not spread into the internal metrics config.

This prevents us from overwriting protocol in development. As a result events are not received by mixpanel. Also I cant turn on the debug / verbose flags to aid my debugging.

[tdumitrescu]

The user-provided config is applied on initialization here: https://github.com/mixpanel/mixpanel-node/blob/e24a3980d0ffbc82e2478c6ac33efbb255a7b1a0/lib/mixpanel-node.js#L453-L455

[phoenixbox]

🤦 whoops, I had something else preventing events being sent, my bad