Unbreak build with Cabal >= 2.4. (#256)

Remove sDistHook, add autogen-modules.

tensorflow-core-ops/Setup.hs

@@ -50,11 +50,6 @@ generatingOpsWrappers = hooks
     , haddockHook = \p l h f -> generateSources l >> haddockHook hooks p l h f
     , replHook = \p l h f args -> generateSources l
                                         >> replHook hooks p l h f args
-    , sDistHook = \p maybe_l h f -> case maybe_l of
-        Nothing -> error "Can't run sdist; run 'cabal configure first."
-        Just l -> do
-                    generateSources l
-                    sDistHook hooks (fudgePackageDesc l p) maybe_l h f
     }
   where
     flagsBuilder dir = OpGenFlags

tensorflow-core-ops/tensorflow-core-ops.cabal

@@ -10,10 +10,11 @@ maintainer:          tensorflow-haskell@googlegroups.com
 copyright:           Google Inc.
 category:            Machine Learning
 build-type:          Custom
-cabal-version:       >=1.24
+cabal-version:       >=2.0
 
 library
   exposed-modules:  TensorFlow.GenOps.Core
+  autogen-modules:  TensorFlow.GenOps.Core
   build-depends:  bytestring
                 , proto-lens >= 0.4.0 && < 0.6.0
                 , tensorflow == 0.2.*