替换数组中的某个

        [self.frenchCoinArray enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if ([[obj objectForKey:@"unit"]isEqualToString:@"USDT"]) {
                dic = obj;
                index = idx;
            }
        }];
        [self.frenchCoinArray removeObjectAtIndex:index];
        [self.frenchCoinArray insertObject:dic atIndex:0];