Fix build errors on GHC 8.2

Author: maoe

GUI/EventsView.hs

@@ -19,12 +19,14 @@ import qualified GUI.GtkExtras as GtkExt
 
 import Control.Monad.Reader
 import Data.Array
+import Data.Monoid
 import Data.IORef
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
 import qualified Data.Text.Lazy.Builder as TB
 import qualified Data.Text.Lazy.Builder.Int as TB (decimal)
 import Numeric
+import Prelude
 
 -------------------------------------------------------------------------------
 

GUI/Timeline/HEC.hs

@@ -20,11 +20,13 @@ import qualified GHC.RTS.Events as GHC
 import Control.Monad
 import qualified Data.IntMap as IM
 import Data.Maybe
+import Data.Monoid
 import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
 import qualified Data.Text.Lazy.Builder as TB
 import qualified Data.Text.Lazy.Builder.Int as TB (decimal)
+import Prelude
 
 renderHEC :: ViewParameters -> Timestamp -> Timestamp
           -> IM.IntMap Text -> (DurationTree,EventTree)