Major bound for servant-server's dependency on servant (#1574)

Reflecting a revision made on hackage for servant-server 0.19.1

Author: alpmestan

servant-server/servant-server.cabal

@@ -72,7 +72,7 @@ library
   -- Servant dependencies
   -- strict dependency as we re-export 'servant' things.
   build-depends:
-      servant             >= 0.19
+      servant             >= 0.19     && < 0.20
     , http-api-data       >= 0.4.1    && < 0.4.4
 
   -- Other dependencies: Lower bound around what is in the latest Stackage LTS.