Allow QuickCheck 2.14 (#1359)

Builds fine and all tests pass.

Author: felixonmars

servant-server/servant-server.cabal

@@ -159,7 +159,7 @@ test-suite spec
     , directory            >= 1.3.0.0  && < 1.4
     , hspec                >= 2.6.0    && < 2.8
     , hspec-wai            >= 0.10.1   && < 0.12
-    , QuickCheck           >= 2.12.6.1 && < 2.14
+    , QuickCheck           >= 2.12.6.1 && < 2.15
     , should-not-typecheck >= 2.1.0    && < 2.2
     , temporary            >= 1.3      && < 1.4
     , wai-extra            >= 3.0.24.3 && < 3.2