fix typo in docs

[mukhtarkv]

Hi. I tried running the following snippet from docs and got the error. According to earlier docs config.exs does not allow calling new/1 function.

  ** (UndefinedFunctionError) function LoggerJSON.Formatters.GoogleCloud.new/1 is undefined (module LoggerJSON.Formatters.GoogleCloud is not available)
      LoggerJSON.Formatters.GoogleCloud.new([metadata: :all, project_id: "logger-101"])

Not sure if the following line should change as well since my change is to rename config.exs to runtime.exs which is for runtime too.