[Minor] Doc strings for `room.moderator?` mention `admin`

[Biep]

In room.rb, the code for moderator? and moderator! has obviously been copied from the corresponding admin methods. However, the search-and-replace has not been fully performed, and the comment lines still mention admin several times.

(BTW, I myself should have written generic power_level? and power_level! methods, and have the admin and moderator methods call those. No code reduplication that way, and people can easily add methods for other power levels that are relevant for them. (E.g. I have a room where postiing rights require a power level of 5, so I might want to add methods for that level too.)

Anyway, none of this is really important.