code: func ClientFromEnv(key string) (*Client, error) {
  	url := os.Getenv(key)
  	return ClientFromURL(url)
  }
docs: /*
  Alternatively, you can instantiate a client from an environment variable.
  This is particularly relevant if you are using Pusher as a Heroku add-on,
  which stores credentials in a `"PUSHER_URL"` environment variable. For example:
  	client := pusher.ClientFromEnv("PUSHER_URL")
  
  */