clarify addition of surreals
errata for 8fa053f
Merge pull request #650 from mikeshulman/surrealaddition

clarify addition of surreals
Mark Errata (auto)
Update cleveref from 0.17.9 to 0.19

I'm trying to get the book to compile with htlatex so that we can have a
nice kindle-compatible epub, and it requires updating cleveref.
(Although I am a fan of MathML and the epubs for #287, e.g., of
@loopspace and @dvanduzer, Kindle doesn't currently support MathML at
all, and htlatex uses embedded images for the math.)
Merge pull request #652 from JasonGross/update-cleveref

Update cleveref from 0.17.9 to 0.19