Contribs: update libass to 0.12.1

(cherry picked from commit 95bf94562cf6ed4e1b43066799e812d322145357)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/ass/SHA512SUMS

-47d6b9b43c549c7f5472c70b32095686d3f0f6c8a16b4c08e4b342532ce51f583855ab43fea93d2dbe8919f85f0ef1acad07d9f43f34e12550f9a4030132c45f  libass-0.12.0.tar.gz
+676f3e64d721426a0de8457f9c5cab77d5a10599ef3008f0660e949dd344c8ce7170cb88656b9b7dad406e878504ab888fb6d38d95061b6320d9fc4ce7f4b03b  libass-0.12.1.tar.gz

contrib/src/ass/rules.mak

 # ASS
-ASS_VERSION := 0.12.0
+ASS_VERSION := 0.12.1
 ASS_URL := https://github.com/libass/libass/releases/download/$(ASS_VERSION)/libass-$(ASS_VERSION).tar.gz
 
 PKGS += ass