Accept any IO object for credentials

[excid3]

This allows passing in credentials either as a file path or IO object. Useful if you're storing your credentials in ENV or Rails credentials for example.

FCM.new("test", "creds.json")
FCM.new("test", StringIO.new("example"))
FCM.new("test", Rails.application.credentials.dig(:google, :credentials))

[sabman]

love it!