Update 01.04.md

[Renzhh]

In the previous code, due to using s[first] and s[second], the program will be crashed with the error "Array subscript is not an integer". Both of "first" and "second" are a pointer to a char.

Code in details:

1. The previous one:

while (first >= s)
    if (s[first--] != s[second++]) 
        return false; // not equal, so it's not apalindrome  

2.After changes:

while (first >= s)
{
    if(*first != *second)
        return false;
    first--;
    second++;
}