message: Fix signature method mistake
diff: NSString *poolRestartRequestJson;
  NSError *ret = [[LedgerUtils sharedInstance] buildPoolRestartRequestWithSubmitterDid:identifier
  action:@"cancel"
  - schedule:nil
  + datetime:nil
  resultJson:&poolRestartRequestJson];
  XCTAssertEqual(ret.code, Success, @"LedgerUtils::buildPoolRestartRequestWithSubmitterDid() failed");
  XCTAssertNotNil(poolRestartRequestJson, @"poolRestartRequestJson is nil!");
  