hledger-interest: re-enable builds
hledger-interest: re-enable builds

The package seems to compile fine with GHC 8.0.1:

  https://travis-ci.org/peti/hledger-interest/builds/136437417

lwm/stackage,christiaanb/stackage,asr/stackage,l29ah/stackage,mstksg/stackage,alanz/stackage,creichert/stackage,peti/stackage,mgajda/stackage,jaspervdj/stackage,judah/stackage,soenkehahn/stackage,Shimuuar/stackage,clinty/stackage,phaazon/stackage,jonschoning/stackage,DanielG/stackage,michalkonecny/stackage,mrkkrp/stackage,int-index/stackage,fimad/stackage,spencerjanssen/stackage,k0ral/stackage,iand675/stackage,Daniel-Diaz/stackage,codedmart/stackage,brendanhay/stackage,stackbuilders/stackage,wereHamster/stackage,ygale/stackage,GregorySchwartz/stackage,ethercrow/stackage,athanclark/stackage,simonmichael/stackage,garetxe/stackage,massysett/stackage,phadej/stackage,fpco/stackage