lnrpc: add WebSocket proxy

go.mod

@@ -26,7 +26,7 @@ require (
 	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
 	github.com/golang/protobuf v1.3.2
 	github.com/google/btree v1.0.0 // indirect
-	github.com/gorilla/websocket v1.4.1 // indirect
+	github.com/gorilla/websocket v1.4.2
 	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
 	github.com/grpc-ecosystem/grpc-gateway v1.14.3