mpris-widget: correct artUrl

Perhaps due to the regex change, or maybe it never did work, art was always
nil. Use gears.string.split(), which works, is much easier to read than the
regex and removes the need to munge the artUrl after too.

mpris-widget/init.lua

@@ -135,24 +135,20 @@ end
 local function worker()
 
     -- retrieve song info
-    local current_song, artist, player_status, art, artUrl
+    local current_song, artist, player_status, artUrl
 
     local update_graphic = function(widget, stdout, _, _, _)
-        local words = {}
-        for w in stdout:gmatch("([^;]*);") do table.insert(words, w) end
-
+        local words = gears.string.split(stdout, ';')
         player_status = words[1]
         artist = words[2]
         current_song = words[3]
-        art = words[4]
+        artUrl = words[4]
         if current_song ~= nil then
             if string.len(current_song) > 18 then
                 current_song = string.sub(current_song, 0, 9) .. ".."
             end
         end
 
-        if art ~= nil then artUrl = string.sub(art, 8, -1) end
-
         if player_status == "Playing" then
             icon.image = PLAY_ICON_NAME
             widget.colors = {beautiful.widget_main_color}