Resolve issue where the stack cannot be located

[shauntarves]

I was trying to use this library in an Express 4 app, and was having trouble with the order_stack function because the stack function was receiving this, but was not looking at the app property of the input argument. I don't know if this is an Express 3 vs 4 thing, but it didn't appear to be.

Either way, this can probably be done cleaner if need be, but this solution worked for me.

[kaifresh]

+1 to this issue. I have found that the issue can be fixed by editing

order_stack(stack(this)); => order_stack(stack(this.app));

Edit: just saw you fixed it with 484e477