fix(01_Introduction): typo
fix(01_Introduction): typo

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