chore: Use new BGS firehose websocket endpoint (#6)

Bluesky has launched their new big graph server in production. In order
to get all posts from all personal data servers the feed generator
should listen to the BGS moving forward.

firehose/firehose.go

@@ -38,7 +38,7 @@ type Firehose struct {
 func New(postChan chan interface{}, context context.Context) *Firehose {
 	dialer := websocket.DefaultDialer
 	firehose := &Firehose{
-		address:  "wss://bsky.social/xrpc/com.atproto.sync.subscribeRepos",
+		address:  "wss://bsky.network/xrpc/com.atproto.sync.subscribeRepos",
 		dialer:   dialer,
 		postChan: postChan,
 		context:  context,