Update with code review suggestions

Author: nilcolor

README.md

@@ -563,6 +563,7 @@ class WeatherTool < MCP::Tool
   )
 end
 ```
+
 Please note: in this case, you must provide `type: "array"`. The default type
 for output schemas is `object`.
 

lib/mcp/tool/output_schema.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-require "json"
 require "json-schema"
 
 module MCP
@@ -33,19 +32,19 @@ def validate_result(result)
 
       private
 
-      def deep_transform_keys(hash, &block)
-        case hash
+      def deep_transform_keys(schema, &block)
+        case schema
         when Hash
-          hash.each_with_object({}) do |(key, value), result|
-            if key.casecmp?("$ref") || key == :$ref
+          schema.each_with_object({}) do |(key, value), result|
+            if key.casecmp?("$ref")
               raise ArgumentError, "Invalid JSON Schema: $ref is not allowed in tool output schemas"
             end
             result[yield(key)] = deep_transform_keys(value, &block)
           end
         when Array
-          hash.map { |e| deep_transform_keys(e, &block) }
+          schema.map { |e| deep_transform_keys(e, &block) }
         else
-          hash
+          schema
         end
       end