Improve relation docs about to_sql and where_values_hash

* User class instead of Users.
* #where_values_hash does not change the value to downcase as the
  example was showing.

[ci skip]

activerecord/lib/active_record/relation.rb

@@ -474,16 +474,16 @@ def reset
 
     # Returns sql statement for the relation.
     #
-    #   Users.where(name: 'Oscar').to_sql
+    #   User.where(name: 'Oscar').to_sql
     #   # => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'
     def to_sql
       @to_sql ||= klass.connection.to_sql(arel, bind_values.dup)
     end
 
-    # Returns a hash of where conditions
+    # Returns a hash of where conditions.
     #
-    #   Users.where(name: 'Oscar').where_values_hash
-    #   # => {name: "oscar"}
+    #   User.where(name: 'Oscar').where_values_hash
+    #   # => {name: "Oscar"}
     def where_values_hash
       equalities = with_default_scope.where_values.grep(Arel::Nodes::Equality).find_all { |node|
         node.left.relation.name == table_name