Fixed Box __repr__ and __str__ AttributeError

[jayfiro]

Added weight=0 to init parameters, self.weight = weight.

[alanbato]

Hi! The reason why self.weight appears in __str__ and __repr__ is because in an older version it was an attribute (just like the one you're adding).
Since there might be other dimensions besides size that you want to limit in your pallet and boxes I included the traits property to hold any amount of such dimensions and limits.
Thus, I removed the weight property so that others could implement it as a trait.

While this fixes the error, (which is good!), I'd be better to remove the self.weight part on the __str__ and __repr__, and instead print out every element on self.traits with its corresponding value.

If you'd be willing to implement such change as part of the PR that'd be great!

[jayfiro]

Thanks for the feedback! Commit 75bc393 should take care of it :)

[alanbato]

Thanks for your contribution!