v1.5.0

• Bumped minimum Elixir version to 1.6
• Raise Pigeon.ConfigError when booting invalid config structs.
  See below for validated keys and error types.
• APNS.JWTConfig now validates key p8 content before connecting.
• Relaxed gen_stage dependency to allow ~> 1.0

Validated config keys:

• ADM.Config - :client_id, :client_secret
• APNS.Config - :cert, :key
• APNS.JWTConfig - :team_id, :key, :key_identifier
• FCM.Config - :key

Possible error values:

• {:error, {:invalid, value}}
• {:error, {:nofile, value}}