Fixed the consistent shape check in convert-to-nested-vectors.

The check that nested vectors had the same shape was incorrect. The bug causes the check to always fail.

A simple test case that creates a Clojure persistent vector with three rows, each a vectorz Vector. The test case assumes that vectorz is the selected implementation.

`(convert-to-nested-vectors (vec (repeat 3 (clojure.core.matrix/new-vector 5)))`