Here this should be working ( at least it does on my server.)
Also make sure you put it in lua/autorun
function donateCommand( pl, text, teamonly )
if (text == "!donate") then
pl:SendLua([[gui.OpenURL("http://bendersvilla.net")]]) -- Change ADDRESS to your chosen page.
for k, v in pairs(player.GetAll()) do v:ChatPrint( "" .. pl:Nick() .. " has gone to !donate." )
end
end
end
hook.Add( "PlayerSay", "ccdonate", donateCommand )