Update nixpkgs pins #2039

Job	Run time
cabal-doExactConfig	9s
runghc	10s
tests-benchmarks	5s
nix-build	10s
unit-tests	8s
build-extra-hackages	9s
check-materialization-concurrency	22s
check-path-support	10s
cabal	8s
closure-size	7s
docs	1m 12s
haskell-nix-roots-do-not-require-IFDs	8s
hix	47s
hydra-ifdLevel-0-and-1	11s
hydra-ifdLevel-3-and-ghc-8-10	6s
hydra-ifdLevel-2	7s
hydra-ifdLevel-3-and-ghc-9-2	8s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	7s
hydra-without-remote-builders	26s
maintainer-scripts	5s
multi-target	9s
shellFor-hoogle	8s
plan-extra-hackages	5s
shellFor-multiple-package	6s
shellFor-not-depends	7s
shellFor-single-package	7s
update-docs	4s
hix-cabal	13s
nix-tools	1m 9s
	7m 3s

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