Move mark from WebSockets down to HTTP

src/HttpResponse.h

@@ -81,6 +81,9 @@ private:
         /* Write status if not already done */
         writeStatus(HTTP_200_OK);
 
+        /* Write mark, this propagates to WebSockets too */
+        writeHeader("Web-Server", "uWebSockets v0.15");
+
         /* If no total size given then assume this chunk is everything */
         if (!totalSize) {
             totalSize = data.length();