Remove ghcSyntaxHighlighter extension

CHANGELOG.md

@@ -6,6 +6,8 @@
   - mmark: 0.0.7.2
   - megaparsec: 0.8
   - clay: 0.14
+- MMark
+  - Remove `ghcSyntaxHighlighter` extension; we already have `skylighting` (which supports more parsers than Haskell)
 
 ## 0.6.0.0
 

src/Rib/Parser/MMark.hs

@@ -83,7 +83,8 @@ exts =
     Ext.mathJax (Just '$'),
     Ext.obfuscateEmail "protected-email",
     Ext.punctuationPrettifier,
-    Ext.ghcSyntaxHighlighter,
+    -- For list of parsers supported, see:
+    -- https://github.com/jgm/skylighting/tree/master/skylighting-core/xml
     Ext.skylighting
   ]