Add Ord instances for Cradle

Language/Haskell/GhcMod/Types.hs

@@ -134,7 +134,7 @@ data Project = CabalProject
              | SandboxProject
              | PlainProject
              | StackProject StackEnv
-               deriving (Eq, Show)
+               deriving (Eq, Show, Ord)
 
 isCabalHelperProject :: Project -> Bool
 isCabalHelperProject StackProject {} = True
@@ -146,7 +146,7 @@ data StackEnv = StackEnv {
     , seBinPath       :: [FilePath]
     , seSnapshotPkgDb :: FilePath
     , seLocalPkgDb    :: FilePath
-    } deriving (Eq, Show)
+    } deriving (Eq, Show, Ord)
 
 -- | The environment where this library is used.
 data Cradle = Cradle {
@@ -161,7 +161,7 @@ data Cradle = Cradle {
   , cradleCabalFile  :: Maybe FilePath
   -- | The build info directory.
   , cradleDistDir    :: FilePath
-  } deriving (Eq, Show)
+  } deriving (Eq, Show, Ord)
 
 data GmStream = GmOutStream | GmErrStream
                 deriving (Show)