Pin index-state used for hls until latest hackage works (#1035)

Author: hamishmack

overlays/hackage-quirks.nix

@@ -65,6 +65,11 @@ in { haskell-nix = prev.haskell-nix // {
       ];
     };
 
+    haskell-language-server = {
+      # Pin for now as current hackage is broken
+      index-state = "2021-02-08T00:00:00Z";
+    };
+
   }."${name}" or {};
 
 }; }