Fix two textual errors in data/lan_server.cfg.

Fix two minor textual errors in the value of the `motd` attribute in
data/lan_server.cfg:

* “Wesnoth” was not capitalized when it ought to have been capitalized.

* “shutdown” was used as a verb. “shutdown” is a noun; the verb is “shut
  down”.
Merge pull request #83 from 8573/fix/text/lan-server-motd-spelling-and-capitalization/1

Fix two textual errors in data/lan_server.cfg.