[Clojure] Change the NDArray Example to use the ndarray formatted printer

[gigasquid]

The Scala package has a new toString method for NDArray that can print out content.

This would be nice to showcase in our NDArray Tutorial.

Example:

user=> (println (str (ndarray/ones [3 3])))
[
 [1.0,1.0,1.0]
 [1.0,1.0,1.0]
 [1.0,1.0,1.0]
]
<NDArray (3,3) cpu(0) float32>
nil
user=> 

https://mxnet.apache.org/api/clojure/index.html
https://mxnet.apache.org/api/clojure/ndarray.html

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