Updated Avoiding pitfalls (markdown)

Avoiding-pitfalls.md

@@ -105,7 +105,7 @@ The simplest solution is to explicitly duplicate the strings in the `JsonBuffer`
     for (int i=0; i<3; i++) {
         char buffer[16];
         sprintf(buffer, "iteration %d", 0);
-        array.add(jsonBuffer.strlen(buffer));
+        array.add(jsonBuffer.strdup(buffer));
     }
     array.printTo(Serial);