Allow QuickCheck 2.14

Builds fine and all tests pass.

Author: felixonmars

servant/servant.cabal

@@ -105,7 +105,7 @@ library
     , http-types             >= 0.12.2   && < 0.13
     , mmorph                 >= 1.1.2    && < 1.2
     , network-uri            >= 2.6.1.0  && < 2.7
-    , QuickCheck             >= 2.12.6.1 && < 2.14
+    , QuickCheck             >= 2.12.6.1 && < 2.15
     , string-conversions     >= 0.4.0.1  && < 0.5
     , tagged                 >= 0.8.6    && < 0.9
     , vault                  >= 0.3.1.2  && < 0.4
@@ -160,7 +160,7 @@ test-suite spec
   -- Additonal dependencies
   build-depends:
       hspec                >= 2.6.0    && < 2.8
-    , QuickCheck           >= 2.12.6.1 && < 2.14
+    , QuickCheck           >= 2.12.6.1 && < 2.15
     , quickcheck-instances >= 0.3.19   && < 0.4
 
   build-tool-depends: