build: Fix 'copy:fastcomposerdemos' task
build: Fix 'copy:fastcomposerdemos' task

It seems that Composer itself now has some dependencies, so we have to
copy the entire vendor/ directory. :(

Change-Id: Id07c006ed69fdf29104d2aff78a535a8083edbe1

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui