Use skylighting 0.9.

pandoc.cabal

@@ -406,8 +406,8 @@ library
                  tagsoup >= 0.14.6 && < 0.15,
                  base64-bytestring >= 0.1 && < 1.2,
                  zlib >= 0.5 && < 0.7,
-                 skylighting >= 0.8.5 && < 0.9,
-                 skylighting-core >= 0.8.5 && < 0.9,
+                 skylighting >= 0.9 && < 0.10,
+                 skylighting-core >= 0.9 && < 0.10,
                  data-default >= 0.4 && < 0.8,
                  temporary >= 1.1 && < 1.4,
                  blaze-html >= 0.9 && < 0.10,

stack.yaml

@@ -16,10 +16,8 @@ extra-deps:
 - pandoc-citeproc-0.17.0.1
 - texmath-0.12.0.2
 - haddock-library-1.9.0
-- skylighting-0.8.5
-- skylighting-core-0.8.5
-- regex-pcre-builtin-0.95.1.2.8.43
-- regex-base-0.94.0.0
+- skylighting-0.9
+- skylighting-core-0.9
 - doclayout-0.3
 - emojis-0.1
 - hslua-1.1.2