Update test: application -> use() should throw if not a function
Update test: application -> use() should throw if not a function

closes #550

Fix lint

Use arrow function

Remove not necessary import

menems/koa,fl0w/koa,koajs/koa,nswbmw/koa,targos/koa,targos/koa,broucz/koa,menems/koa,fl0w/koa,broucz/koa