chore(hott) fix markup syntax in book.md
chore(hott) fix markup syntax in book.md

soonhokong/lean,soonhokong/lean,fpvandoorn/lean2,fpvandoorn/lean2,fpvandoorn/lean2,soonhokong/lean,fpvandoorn/lean2,soonhokong/lean,soonhokong/lean,fpvandoorn/lean2