fix(js/main_live.js): use relative path for bg images
fix(js/main_live.js): use relative path for bg images

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