[ #1222 ] Re-enable Agda.
[ #1222 ] Re-enable Agda.

Added support for unordered-containers 0.2.6.0 in Agda 2.5.1.

Gabriel439/stackage,fpco/stackage,phadej/stackage,simonmichael/stackage,marcinmrotek/stackage,bartavelle/stackage,agrafix/stackage,mstksg/stackage,peti/stackage,int-index/stackage,Daniel-Diaz/stackage,k0ral/stackage,alanz/stackage,lwm/stackage,l29ah/stackage,clinty/stackage,jaspervdj/stackage,soenkehahn/stackage,nomeata/stackage,jonschoning/stackage,christiaanb/stackage,stackbuilders/stackage,wereHamster/stackage,athanclark/stackage,GregorySchwartz/stackage,ethercrow/stackage,asr/stackage,mrkkrp/stackage,creichert/stackage,mgajda/stackage,codedmart/stackage,fimad/stackage,brendanhay/stackage,michalkonecny/stackage,Shimuuar/stackage,garetxe/stackage,judah/stackage,DanielG/stackage,ygale/stackage,phaazon/stackage,iand675/stackage,spencerjanssen/stackage,massysett/stackage