Add test for custom tokenizer serialization (resolves #2494)
Add test for custom tokenizer serialization (resolves #2494)

honnibal/spaCy,spacy-io/spaCy,spacy-io/spaCy,spacy-io/spaCy,honnibal/spaCy,spacy-io/spaCy,honnibal/spaCy,explosion/spaCy,explosion/spaCy,explosion/spaCy,explosion/spaCy,spacy-io/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy,spacy-io/spaCy