[pitivi] Update gst-transcoder to 1.12.1

[Thibault Saunier <tsaunier src gnome org>]

commit 245cf1bf2f44ea13f82d7ed4efbff78cb12f2def
Author: Thibault Saunier <tsaunier gnome org>
Date:   Mon Jul 17 10:43:52 2017 -0400

    Update gst-transcoder to 1.12.1

 subprojects/gst-transcoder |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/subprojects/gst-transcoder b/subprojects/gst-transcoder
index 19292c6..79c2c39 160000
--- a/subprojects/gst-transcoder
+++ b/subprojects/gst-transcoder
@@ -1 +1 @@
-Subproject commit 19292c6acb31484ae6b554cf972ffcfbbba0f12b
+Subproject commit 79c2c390b9226fe1f137f08382787abee5f7ee6e