Update SWI-Prolog to 7.7.8 and stable to 7.6.4.

library/swipl

@@ -1,11 +1,10 @@
 Maintainers: Dave Curylo <[email protected]> (@ninjarobot)
 GitRepo: https://github.com/SWI-Prolog/docker-swipl.git
-GitCommit: 2fbb0429d19cf02b3332432124b349c62397fa5c
+GitCommit: 42160906df31e8bb72d1d4222aaecafd1ff1a405
 
-Tags: latest, 7.7.7
+Tags: latest, 7.7.8
 Architectures: amd64, arm32v7
-Directory: 7.7.7/stretch
+Directory: 7.7.8/stretch
 
-Tags: stable, 7.6.3
-GitCommit: 2fbb0429d19cf02b3332432124b349c62397fa5c
-Directory: 7.6.3/stretch
+Tags: stable, 7.6.4
+Directory: 7.6.4/stretch