Bump blaze-markup, blaze-html lower bounds to 0.8, 0.9.

This is needed because the type constructor Empty in MarkupM
has changed, and the HTML writer assumes the constructor has
an argument.

Closes #4334.

pandoc.cabal

@@ -372,8 +372,8 @@ library
                  skylighting >= 0.5.1 && < 0.7,
                  data-default >= 0.4 && < 0.8,
                  temporary >= 1.1 && < 1.3,
-                 blaze-html >= 0.5 && < 0.10,
-                 blaze-markup >= 0.5.1 && < 0.9,
+                 blaze-html >= 0.9 && < 0.10,
+                 blaze-markup >= 0.8 && < 0.9,
                  yaml >= 0.8.8.2 && < 0.9,
                  scientific >= 0.2 && < 0.4,
                  vector >= 0.10 && < 0.13,