Correct month name for is_IS locale (Debian bug #178513)

[Petter Reinholdtsen]

[Keld Jørn Simonsen]
> It is my information that day and month names are written with an initial
> lower case letter in correct Icelandic. My reference is the "Nordic
> Cultural Requirements on Information Technology" published by the
> Icelandic standradization body STRI 1992.
> 
> The change proposed here is thus incorrect.

The proposed change is to _not_ use capital letters, ie lower case
letters.  It is thus correct.  Thanks for verifying this. :)