fix thumbnail link to be github raw url
fix thumbnail link to be github raw url

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