devel/stack: Update to 1.5.1
- This late port update fixes using Stackage Nightly snapshots >= 2017-07-31 (which use GHC 8.2.1) with Stack
- Fix iconv dependency and use iconv:translit like all the other Haskell ports since GHC 8.0.2 was imported in r447548
MFH: 2017Q4