Change opcode to text for websocket

This means that we can see the json in chrome to debug it.

Change-Id: I74394367bba4fbafcef1c3b929f34d470ab1da92
diff --git a/y2019/vision/server/server.cc b/y2019/vision/server/server.cc
index bbd24fc..e531f51 100644
--- a/y2019/vision/server/server.cc
+++ b/y2019/vision/server/server.cc
@@ -60,8 +60,7 @@
 
 void WebsocketHandler::SendData(const std::string &data) {
   for (seasocks::WebSocket *websocket : connections_) {
-    websocket->send(reinterpret_cast<const uint8_t *>(data.data()),
-                    data.size());
+    websocket->send(data.c_str());
   }
 }