Add pin for pyrsistent<0.17.0 (#6116)
Add pin for pyrsistent<0.17.0 (#6116)

Add pin for pyrsistent<0.17.0 since pyrsistent>=0.17.1 is only
compatible with python3.5+.
honnibal/spaCy,honnibal/spaCy,spacy-io/spaCy,spacy-io/spaCy,explosion/spaCy,explosion/spaCy,explosion/spaCy,explosion/spaCy,spacy-io/spaCy,explosion/spaCy,spacy-io/spaCy,explosion/spaCy,honnibal/spaCy,honnibal/spaCy,spacy-io/spaCy,spacy-io/spaCy