Update codecs dependency, fix warning

Author: garyb

bower.json

@@ -21,7 +21,7 @@
   },
   "license": "MIT",
   "dependencies": {
-    "purescript-argonaut-codecs": "^0.4.1",
+    "purescript-argonaut-codecs": "^0.5.0",
     "purescript-profunctor-lenses": "^0.3.3"
   },
   "devDependencies": {

src/Data/Argonaut/JCursor.purs

@@ -9,7 +9,7 @@ import Data.Either (Either(..))
 import Data.Foldable (foldl)
 import Data.List (List(), zipWith, range, head, singleton, toList)
 import Data.Maybe (Maybe(..), fromMaybe, maybe)
-import Data.Monoid (Monoid, mempty)
+import Data.Monoid (Monoid)
 import Data.Tuple (Tuple(..), fst, snd)
 
 import qualified Data.Array as A