fix(03): fix typo
fix(03): fix typo

soonhokong/lean-tutorial,soonhokong/lean-tutorial,cjmazey/fork_leanprover_tutorial,cjmazey/fork_leanprover_tutorial,avigad/tutorial,cjmazey/fork_leanprover_tutorial,avigad/tutorial,leanprover/tutorial,soonhokong/lean-tutorial,leanprover/tutorial,fpvandoorn/tutorial,fpvandoorn/tutorial,avigad/tutorial,Hodapp87/cs6460_project,Hodapp87/cs6460_project,fpvandoorn/tutorial,leanprover/tutorial,Hodapp87/cs6460_project