code: public VaadinForHeroku withApplicationListener(final String... listeners){
          checkVarArgsArguments(listeners);
          this.applicationListeners.addAll(Arrays.asList(listeners));
          return self();
      }
docs: Add an application listener to the configuration of the server.
  
  @param listeners the application listener(s) to add to the server configuration.
  @since 0.3