Remove this from line #2:
[url][/url]
So it should look like this:
function ulx.getaddons( calling_ply )
calling_ply:SendLua("gui.OpenURL('http://steamcommunity.com/sharedfiles/filedetails/?id=295885854')")
end
local getaddons = ulx.command( "Custom", "ulx getaddons", ulx.getaddons, "!getaddons" )
getaddons:defaultAccess( ULib.ACCESS_ALL )
getaddons:help( "Opens the page of our addon collection" )