parse negation properly.

diff --git a/src/prolog/parser b/src/prolog/parser
index 29423d92d8793cbc82f686df4ac24cd9a0dd11d6..87d0d493e69e5cde80f454d21f8caa33cbffca3e 160000 (submodule)
--- a/src/prolog/parser
+++ b/src/prolog/parser
@@ -1 +1 @@
-Subproject commit 29423d92d8793cbc82f686df4ac24cd9a0dd11d6
+Subproject commit 87d0d493e69e5cde80f454d21f8caa33cbffca3e