* Update stack.yaml to lts-12.26 (GHC 8.4.4) with simplified nix config
(On GHC 8.6.5, profiled build was exiting with:
-- While building package postgrest-5.2.0 using:
/home/circleci/.stack/setup-exe-cache/x86_64-linux/Cabal-simple_mPHDZzAJ_2.4.0.1_ghc-8.6.5 --builddir=.stack-work/dist/x86_64-linux/Cabal-2.4.0.1 build lib:postgrest exe:postgrest --ghc-options " -ddump-hi -ddump-to-file -fdiagnostics-color=always"
Process exited with code: ExitFailure (-9) (THIS MAY INDICATE OUT OF MEMORY)
Exited with code 1)
* stack.yaml: Add postgresql to nix packages
