Fixed malformed code in RNN example#21

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s-m-e wants to merge 2 commits intoroatienza:masterfrom

Commits on Apr 7, 2019

referencing length of a dict inside a for loop, which is changing the dict itself, is error-prone
s-m-e
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accessing keys and values of a dict separately can fail - order is not guaranteed to be stable between calls
s-m-e
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