Update an example on the website

[Walter Bright]

biozic wrote:
> In http://www.digitalmars.com/d/2.0/declaration.html#AutoDeclaration, 
> shouldn't the code:
>     auto s = "string"; // s is type immutable(char)[6]
> be updated to:
>     auto s = "string"; // s is type immutable(char)[]
> ?

Yes, good catch!