Import transitional MonadFail where necessary for older GHCs

Author: ali-abrar

src/Nix/Fresh/Stable.hs

@@ -14,6 +14,7 @@ import Nix.Effects
 import Nix.Render
 import Nix.Thunk
 import Nix.Thunk.StableId
+import Control.Monad.Fail
 import Control.Monad.Reader
 import Control.Monad.State.Strict
 import Control.Monad.Ref

src/Nix/Scope/Basic.hs

@@ -19,6 +19,7 @@ module Nix.Scope.Basic where
 
 import Control.Applicative
 import Control.Monad.Exception
+import Control.Monad.Fail
 import Control.Monad.Reader
 import Control.Monad.State
 import Control.Monad.Catch

src/Nix/Thunk/Basic.hs

@@ -18,6 +18,7 @@ module Nix.Thunk.Basic (ThunkT (..), runThunkT, NThunkF (..), Deferred (..)) whe
 
 import           Control.Exception       hiding ( catch )
 import           Control.Monad.Catch
+import           Control.Monad.Fail
 import           Control.Monad.Reader
 import           Control.Monad.State