Merge pull request #25 from tvh/ghc84-fix

Some fixes for GHC 8.4

Author: ameingast

postgresql-simple-migration.cabal

@@ -70,5 +70,5 @@ test-suite tests
     build-depends:          base                        >= 4.6      && < 5.0,
                             bytestring                  >= 0.10     && < 0.11,
                             postgresql-simple           >= 0.4      && < 0.6,
-                            hspec                       >= 2.2      && < 2.5,
+                            hspec                       >= 2.2      && < 2.6,
                             postgresql-simple-migration

src/Database/PostgreSQL/Simple/Migration.hs

@@ -255,6 +255,11 @@ data MigrationCommand
     -- ^ Performs a series of 'MigrationCommand's in sequence.
     deriving (Show, Eq, Read, Ord)
 
+#if __GLASGOW_HASKELL__ >= 804
+instance Semigroup MigrationCommand where
+    (<>) = mappend
+#endif
+
 instance Monoid MigrationCommand where
     mempty = MigrationCommands []
     mappend (MigrationCommands xs) (MigrationCommands ys) = MigrationCommands (xs ++ ys)