Switch default train corpus max_length to 0 in quickstart (#8142)
Switch default train corpus max_length to 0 in quickstart (#8142)

The behavior of `spacy.Corpus.v1` is unexpected enough for `max_length
!= 0` that `0` is a better default for users creating a new config with
the quickstart.

If not, documents are skipped, sometimes the entire corpus is skipped,
and sometimes documents are (quite unexpectedly for your average user)
split into sentences.
explosion/spaCy,honnibal/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy,explosion/spaCy,honnibal/spaCy,explosion/spaCy,explosion/spaCy,honnibal/spaCy