Custom snapshot and explicit lower bounds

[fizruk]

• Custom snapshot is used to speedup builds on CI (avoid rebuilding lsp in particular)
• Lower bounds are taken from Stackage LTS 13.1 (the earliest LTS for GHC 8.6).

Funnily enough, GHC panics when trying to build the old version:

stack build --stack-yaml=stack-8.6.5.yaml

ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.5 for x86_64-apple-darwin):
        Prelude.chr: bad argument: 3179719811

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug


Error: [S-6374]
       While building simple Setup.hs (scroll up to its section to see the error) using:
       /Users/nikolaikudasov/.stack/programs/x86_64-osx/ghc-8.6.5/bin/ghc-8.6.5 -rtsopts -threaded -clear-package-db -global-package-db -hide-all-packages -package base -main-is StackSetupShim.mainOverride -package Cabal-2.4.0.1 /Users/nikolaikudasov/.stack/setup-exe-src/setup-6HauvNHV.hs /Users/nikolaikudasov/.stack/setup-exe-src/setup-shim-6HauvNHV.hs -o /Users/nikolaikudasov/.stack/setup-exe-cache/x86_64-osx/tmp-Cabal-simple_6HauvNHV_2.4.0.1_ghc-8.6.5
       Process exited with code: ExitFailure 1