Fix crash when skeleton kills player using bow

Commit 5252952555 used string.gsub() to
strip newlines from tools in death messages. The second return value of
string.gsub() (the number of substitutions) was erroneously returned too
by get_tool_name(). This bug caused a crash whenever a skeleton killed a
player using its bow.

mods/HUD/mcl_death_messages/init.lua

@@ -7,7 +7,8 @@ local function get_tool_name(item)
 		local def = item:get_definition()
 		name=def._tt_original_description or def.description
 	end
-	return name:gsub("[\r\n]"," ")
+	local sanitized_name, substitution_count = name:gsub("[\r\n]"," ")
+	return sanitized_name
   end
 
 mcl_death_messages = {}