Replace `\autoref` with `\cref` throughout.
Fix proof of theorem 7.7.4
Merge branch 'master' of github.com:HoTT/book

Conflicts:
	errata.tex    .... there was an \autoref
Merge pull request #668 from andrejbauer/master

Replace `\autoref` with `\cref` throughout.
more details in proof of 7.7.4
Merge pull request #669 from KevinQuirin/th774

Fix proof of theorem 7.7.4
fix grammar in 7.7.4