re-enable hledger packages
re-enable hledger packages

They got quietly removed 3 weeks ago by #3093. 
The current 1.5 versions all seem to build fine with haskell-src-exts-1.20.1.
garetxe/stackage,wereHamster/stackage,stackbuilders/stackage,soenkehahn/stackage,mstksg/stackage,mrkkrp/stackage,ethercrow/stackage,creichert/stackage,peti/stackage,simonmichael/stackage,asr/stackage,massysett/stackage,iand675/stackage,jonschoning/stackage,spencerjanssen/stackage,michalkonecny/stackage,clinty/stackage,Shimuuar/stackage,lwm/stackage,fpco/stackage,Daniel-Diaz/stackage,phaazon/stackage,athanclark/stackage,fimad/stackage,mgajda/stackage,int-index/stackage