Adjust wording according to the 2021 specification

src/Language/GraphQL/Validate/Rules.hs

@@ -856,8 +856,8 @@ knownArgumentNamesRule = ArgumentsRule fieldRule directiveRule
         , "\"."
         ]
 
--- | GraphQL servers define what directives they support. For each usage of a
--- directive, the directive must be available on that server.
+-- | GraphQL services define what directives they support. For each usage of a
+-- directive, the directive must be available on that service.
 knownDirectiveNamesRule :: Rule m
 knownDirectiveNamesRule = DirectivesRule $ const $ \directives' -> do
     definitions' <- asks $ Schema.directives . schema
@@ -909,9 +909,9 @@ knownInputFieldNamesRule = ValueRule go constGo
         , "\"."
         ]
 
--- | GraphQL servers define what directives they support and where they support
+-- | GraphQL services define what directives they support and where they support
 -- them. For each usage of a directive, the directive must be used in a location
--- that the server has declared support for.
+-- that the service has declared support for.
 directivesInValidLocationsRule :: Rule m
 directivesInValidLocationsRule = DirectivesRule directivesRule
   where