only add HasGenRequest instance for Fragment on >=0.18.2

Author: amesgen

servant-quickcheck/src/Servant/QuickCheck/Internal/HasGenRequest.hs

@@ -196,5 +196,7 @@ instance (HasGenRequest a) => HasGenRequest (WithNamedContext x y a) where
 instance (HasGenRequest a) => HasGenRequest (BasicAuth x y :> a) where
     genRequest _ = genRequest (Proxy :: Proxy a)
 
+#if MIN_VERSION_servant(0,18,2)
 instance (HasGenRequest a) => HasGenRequest (Fragment v :> a) where
     genRequest _ = genRequest (Proxy :: Proxy a)
+#endif