resolver: lts-21.20

extra-deps:
 - GenericPretty-1.2.2
 - clash-ghc-1.8.1
 - clash-prelude-1.8.1
 - clash-lib-1.8.1
 - concurrent-supply-0.1.8
 - prettyprinter-interp-0.2.0.0
 - pretty-show-1.10