Add LTS Haskell 3.20.

+3
+3
pkgs/top-level/haskell-packages.nix
··· 313 lts-3_19 = packages.ghc7102.override { 314 packageSetConfig = callPackage ../development/haskell-modules/configuration-lts-3.19.nix { }; 315 }; 316 317 }; 318 }
··· 313 lts-3_19 = packages.ghc7102.override { 314 packageSetConfig = callPackage ../development/haskell-modules/configuration-lts-3.19.nix { }; 315 }; 316 + lts-3_20 = packages.ghc7102.override { 317 + packageSetConfig = callPackage ../development/haskell-modules/configuration-lts-3.20.nix { }; 318 + }; 319 320 }; 321 }