Remove capacity from JsonDocument's constructor

examples/JsonUdpBeacon/JsonUdpBeacon.ino

@@ -48,7 +48,7 @@ void setup() {
 void loop() {
   // Allocate a temporary JsonDocument
   // Use https://arduinojson.org/v6/assistant to compute the capacity.
-  JsonDocument doc(500);
+  JsonDocument doc;
 
   // Create the "analog" array
   JsonArray analogValues = doc.createNestedArray("analog");