[ci skip] fix doc for the Hash#assert_valid_keys

activesupport/lib/active_support/core_ext/hash/keys.rb

@@ -57,9 +57,9 @@ def symbolize_keys!
   end
   alias_method :to_options!, :symbolize_keys!
 
-  # Validate all keys in a hash match <tt>*valid_keys</tt>, raising ArgumentError
-  # on a mismatch. Note that keys are NOT treated indifferently, meaning if you
-  # use strings for keys but assert symbols as keys, this will fail.
+  # Ensures all the hash's keys are present in the supplied list of <tt>*valid_keys</tt>.
+  # Raises an ArgumentError if any unexpected keys are encountered. 
+  # Note that keys are NOT treated indifferently: strings and symbols will not match each other.
   #
   #   { name: 'Rob', years: '28' }.assert_valid_keys(:name, :age) # => raises "ArgumentError: Unknown key: :years. Valid keys are: :name, :age"
   #   { name: 'Rob', age: '28' }.assert_valid_keys('name', 'age') # => raises "ArgumentError: Unknown key: :name. Valid keys are: 'name', 'age'"