upgrade to LTS 19.8 (GHC 9.0.2)

Also add `+RTS --io-manager=native -RTS` to the `ghc-options`.  Need
someone on Windows to check whether this resolves #253.

disco.cabal

@@ -484,6 +484,7 @@ executable disco
   import:              common
   hs-source-dirs:      repl
   main-is:             REPL.hs
+  ghc-options:         +RTS --io-manager=native -RTS
   build-depends:       base,
                        disco,
                        directory,

stack.yaml

@@ -2,23 +2,17 @@
 # For more information, see: http://docs.haskellstack.org/en/stable/yaml_configuration/
 
 # Specifies the GHC version and set of packages available (e.g., lts-3.5, nightly-2015-09-21, ghc-7.10.2)
-resolver: lts-18.13
+resolver: lts-19.8
 
 # Local packages, usually specified by relative directory name
 packages:
   - "."
 
 # Packages to be pulled from upstream that are not in the resolver (e.g., acme-missiles-0.3)
 extra-deps:
-  - unbound-generics-0.4.0
-  - simple-enumeration-0.2
-  - oeis-0.3.10
-  - capability-0.4.0.0@sha256:d86d85a1691ef0165c77c47ea72eac75c99d21fb82947efe8b2f758991cf1837,3345
-  - polysemy-1.6.0.0@sha256:29a73b1bf3d0049b12041016b7ee25e76bd8f6e99f9c37c2dde2b46368246697,6184
-  - polysemy-plugin-0.4.0.0
-  - polysemy-zoo-0.7.0.1@sha256:60c2921df95f61d43222a75adde4f330e9510320b416132838a354cd81b4bcc5,3846
-  - compact-0.2.0.0@sha256:75ef98cb51201b4a0d6de95cbbb62be6237c092a3d594737346c70c5d56c2380,2413
+  - polysemy-zoo-0.8.0.0@sha256:902bb663a6ae7151e548727dd91a8d642fc6ed0dcd7b312aac8d75e37013e638,3880
   - constraints-0.12   # needed since polysemy-zoo hasn't updated upper bound to allow 0.13
+  - simple-enumeration-0.2.1@sha256:8625b269c1650d3dd0e3887351c153049f4369853e0d525219e07480ea004b9f,1178
 
 # Override default flag values for local packages and extra-deps
 flags: {}