* Bug fix to ADADELTA: on first iteration, RMS of the update should be eta, not zero.
* Bug fix to ADADELTA: on first iteration, RMS of the update should be eta, not zero.

spacy-io/thinc,spacy-io/thinc,spacy-io/thinc,explosion/thinc,explosion/thinc,explosion/thinc,explosion/thinc