haskellPackages.cmark: allow text == 2.0.*

I've verified that the (small) test suite still passed and had a cursory
look at the code for the bindings. cmark doesn't use any internal Text
modules nor seems to make any specific assumptions about Text's internal
encoding. The interfaces used are Data.Text.Encoding and
Data.Text.Foreign. From the latter, only functions relating to CString
are used which have used UTF-8 encoding already for text < 2.0. (It
stands to reason that cmark may actually benefit from the internal
encoding change in 2.0.)

pkgs/development/haskell-modules/configuration-common.nix

@@ -219,6 +219,10 @@ self: super: {
   # There are numerical tests on random data, that may fail occasionally
   lapack = dontCheck super.lapack;
 
+  # Allow text-2.0.*
+  # https://github.com/jgm/cmark-hs/pull/15
+  cmark = doJailbreak super.cmark;
+
   # fix tests failure for base≥4.15 (https://github.com/kim/leveldb-haskell/pull/41)
   leveldb-haskell = appendPatch (fetchpatch {
     url = "https://github.com/kim/leveldb-haskell/commit/f5249081f589233890ddb1945ec548ca9fb717cf.patch";