GF.Server: add 'import Control.Applicative' for compatibilit with GHC<7.10

One could also add stricter version constraints in gf.cabal, e.g.
base>=4.8 (implies GHC>=7.10) if we want to only support building with
GHC>=7.10.

src/compiler/GF/Server.hs

@@ -3,6 +3,7 @@
 module GF.Server(server) where
 import Data.List(partition,stripPrefix,isInfixOf)
 import qualified Data.Map as M
+import Control.Applicative -- for GHC<7.10
 import Control.Monad(when)
 import Control.Monad.State(StateT(..),get,gets,put)
 import Control.Monad.Error(ErrorT(..),Error(..))