chore(header/header.tex): bump copyright year
chore(header/header.tex): bump copyright year

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