Make token.lemma property return hash instead of unicode

[thomasopsomer]

Description

token.lemma wasn't always returning an integer ! When the lemma wasn't set on the c attribute, the lemma property calls the lemmatizer lookup table but it returned the unicode instead of the hash.

Small fix, but quite annoying bug ^^.

Types of change

bug fix

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[honnibal]

Thanks!