Raise tagsoup lower bound to 0.13.7.

This fixes entity-related problems.

Closes #2734.

pandoc.cabal

@@ -261,7 +261,7 @@ Library
                  extensible-exceptions >= 0.1 && < 0.2,
                  pandoc-types >= 1.16 && < 1.17,
                  aeson >= 0.7 && < 0.12,
-                 tagsoup >= 0.13.1 && < 0.14,
+                 tagsoup >= 0.13.7 && < 0.14,
                  base64-bytestring >= 0.1 && < 1.1,
                  zlib >= 0.5 && < 0.7,
                  highlighting-kate >= 0.6.1 && < 0.7,