code: public static String getsignkey(String mch_id, String partnerKey) {
  		Map<String, String> map = new HashMap<String, String>();
  		String nonce_str = String.valueOf(System.currentTimeMillis());
  		map.put("mch_id", mch_id);
  		map.put("nonce_str", nonce_str);
  		map.put("sign", PaymentKit.createSign(map, partnerKey));
  		return doPost(GETSINGKEY, map);
  	}
docs: 获取验签秘钥API
  
  @param mch_id
  商户号
  @param partnerKey
  密钥
  @return {String}