Fix error in Member:getPermissions()

[RiskoZoSlovenska]

In Member.lua on lines 220-221, we index a number, leading to an error whenever Member:getPermissions() is called:

local allow, deny = 0, 0
for role in self.roles:iter() do
    if role.id ~= guild.id then -- just in case
        local overwrite = overwrites:get(role.id)
        if overwrite then
            deny = deny:union(overwrite:getDeniedPermissions())
            allow = allow:union(overwrite:getAllowedPermissions())
        end
    end
end

Looks like this was caused by https://github.com/SinisterRectus/Discordia/commit/6493e89d787199b592c6b1fbb8f562487030053f, when numbers were swapped out for objects. This PR fixes the error by replacing the values of allow and deny with blank Permissions objects.

[SinisterRectus]

Looks good to me, thank you!