create our cache and lib directory always with mode 755

create our cache and lib directory always with mode 755

We autocreate for a while now the last two directories in /var/lib/apt/lists
(similar for /var/cache/apt/archives) which is very nice for systems having
any of those on tmpfs or other non-persistent storage. This also means
though that this creation is effected by the default umask, so for
people with aggressive umasks like 027 the directories will be created
with 750, which means all non-root users are left out, which is usually
exactly what we want then this umask is set, but the cache and lib
directories contain public knowledge. There isn't any need to protect
them from viewers and they render apt completely useless if not
readable.