Fix tests

[lucashpandolfo]

Two tests were failing due to stopwords functionality.

I am not sure about add-indexes method. I jut don't know. (elt indexes 0) was failing because indexes was a vector instead of a list, but i'm pretty sure elt should work for vectors too. 😱
¿Ideas?

[PuercoPop]

@lucashpandolfo: Scymtym points the reason why SBCL chokes on add-indexes is because SBCL assumes indexes (as a &rest parameter) is bound to a list. This can be fixed with a (declare (cl:optimize (safety 3))), but it would be better to rewrite the funciton

<scymtym> PuercoPop: the (montezuma:add-indexes index) method assigns
                a vector value to the &rest parameter. SBCL seems to assume
                that the variable will only be bound to list values
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