Bug: LINE Bridge Missing Network Icon

At the following location, the bridge doesn't have a network icon defined. This causes [mautrix-manager](https://github.com/mautrix/manager) to puke when trying to load the list of bridges available on a server.

https://github.com/beeper/line/blob/1bff055219c9f01a9bd1cd106411e4ce868c00b8/pkg/connector/connector.go#L89