Merge pull request rails#15446 from akshay-vishnoi/doc_changes

[ci skip] Correct documentation of HashWithIndifferentAccess#dup

Author: robin850

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -182,8 +182,8 @@ def values_at(*indices)
     #   dup  = hash.dup
     #   dup[:a][:c] = 'c'
     #
-    #   hash[:a][:c] #=> "c"
-    #   dup[:a][:c]  #=> "c"
+    #   hash[:a][:c] # => nil
+    #   dup[:a][:c]  # => "c"
     def dup
       self.class.new(self).tap do |new_hash|
         new_hash.default = default