ios <__NSArrayM: 0x600003f27270

 for (id item in tmp) 

简单来说就是for循环的时候不能改变里面的值，改变就会报错

解决方法：
1.
 [arr2 enumerateObjectsUsingBlock:^(NSMutableDictionary *obj, NSUInteger idx, BOOL *stop) {
            if ([obj[@"a"] isEqualToString:@"3"]) {
                *stop = YES;
                [arr2 removeObject:obj]; // or obj[@"a"] = @"4ewewewe";
            }
        }];
2.
 NSArray *tmp = [NSArray arrayWithArray:arr2];
        for (NSMutableDictionary *s in tmp) {
            if ([s[@"a"] isEqualToString:@"3"]) {
                s[@"a"] = @"eeee";
                [arr2 removeObject:s];
            }
        }