Fix the span doc typo
Fix the span doc typo

Fix the typo in the span API doc.
It explains the `end` of the span as the `start_char` description.
explosion/spaCy,banglakit/spaCy,recognai/spaCy,oroszgy/spaCy.hu,spacy-io/spaCy,raphael0202/spaCy,banglakit/spaCy,honnibal/spaCy,aikramer2/spaCy,honnibal/spaCy,Gregory-Howard/spaCy,Gregory-Howard/spaCy,aikramer2/spaCy,oroszgy/spaCy.hu,explosion/spaCy,aikramer2/spaCy,oroszgy/spaCy.hu,recognai/spaCy,recognai/spaCy,Gregory-Howard/spaCy,spacy-io/spaCy,oroszgy/spaCy.hu,spacy-io/spaCy,spacy-io/spaCy,oroszgy/spaCy.hu,explosion/spaCy,honnibal/spaCy,explosion/spaCy,recognai/spaCy,raphael0202/spaCy,recognai/spaCy,raphael0202/spaCy,explosion/spaCy,raphael0202/spaCy,explosion/spaCy,banglakit/spaCy,recognai/spaCy,aikramer2/spaCy,spacy-io/spaCy,raphael0202/spaCy,raphael0202/spaCy,aikramer2/spaCy,Gregory-Howard/spaCy,oroszgy/spaCy.hu,Gregory-Howard/spaCy,honnibal/spaCy,spacy-io/spaCy,Gregory-Howard/spaCy,aikramer2/spaCy,banglakit/spaCy,banglakit/spaCy,banglakit/spaCy