[gnome-books/wip/hadess/more-dead-code-cleanup] libgd: Update libgd

[Bastien Nocera <hadess src gnome org>]

commit cdb7bc73ca3e8d54502afbbbb5b342f095426177
Author: Bastien Nocera <hadess hadess net>
Date:   Mon Jan 28 17:19:17 2019 +0100

    libgd: Update libgd

 subprojects/libgd | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/subprojects/libgd b/subprojects/libgd
index 039eff81..c7c7ff4e 160000
--- a/subprojects/libgd
+++ b/subprojects/libgd
@@ -1 +1 @@
-Subproject commit 039eff81546b1076bcad5eab5ee6bc37e702e0a5
+Subproject commit c7c7ff4e05d3fe82854219091cf116cce6b19de0