chore(category_theory/closed/cartesian): style (#3098)
chore(category_theory/closed/cartesian): style (#3098)

Just breaking long lines, and using braces in a multi-goal proof, for a recently added file.
 (#2894)



Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib