Fixed issue resolving response $refs

Author: darrelmiller

src/Microsoft.OpenApi.Readers/Services/OpenApiReferenceResolver.cs

@@ -83,7 +83,7 @@ public override void Visit(IDictionary<string, OpenApiExample> examples)
         /// <summary>
         /// Resolve all references to responses
         /// </summary>
-        public override void Visit(IDictionary<string, OpenApiResponse> responses)
+        public override void Visit(OpenApiResponses responses)
         {
             ResolveMap(responses);
         }

src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs

@@ -144,12 +144,6 @@ public virtual void Visit(OpenApiRequestBody requestBody)
         {
         }
 
-        /// <summary>
-        /// Visits responses.
-        /// </summary>
-        public virtual void Visit(IDictionary<string, OpenApiResponse> responses)
-        {
-        }
 
         /// <summary>
         /// Visits headers.