[pitivi] layer: Use symbolic icons for layer type

[Alexandru Băluț <alexbalut src gnome org>]

commit 5a3406979674b348d47734682bdfc0265d3ae0cd
Author: Diego Garcia Gangl <dnicolas gmail com>
Date:   Fri Apr 12 20:44:08 2019 -0300

    layer: Use symbolic icons for layer type

 pitivi/timeline/layer.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/timeline/layer.py b/pitivi/timeline/layer.py
index 9e0b7a43..c94cf008 100644
--- a/pitivi/timeline/layer.py
+++ b/pitivi/timeline/layer.py
@@ -220,10 +220,10 @@ class LayerControls(Gtk.EventBox, Loggable):
 
         if media_types & GES.TrackType.VIDEO or not media_types:
             # The layer has video or is empty.
-            icon = "video-x-generic"
+            icon = "video-x-generic-symbolic"
         else:
             # The layer has audio and nothing else.
-            icon = "audio-x-generic"
+            icon = "audio-x-generic-symbolic"
 
         if icon != self.__icon:
             image = Gtk.Image.new_from_icon_name(icon, Gtk.IconSize.BUTTON)