code: private static Collection<Header> getStandardHeaders() {
          Collection<Header> colHeaders = new Vector<Header>();
          colHeaders.add(new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));
          colHeaders.add(new BasicHeader(HTTP.USER_AGENT, "MercadoPago Java SDK/1.0.10"));
          colHeaders.add(new BasicHeader("x-product-id", "BC32A7VTRPP001U8NHJ0"));
          return colHeaders;
      }
docs: Returns standard headers for all the requests
  
  @return              a collection with headers objects