Fix error when using `with_options` with lambda.

It was causing error when using `with_options` passing a lambda as its
last argument.

    class User < ActiveRecord::Base
      with_options dependent: :destroy do |assoc|
        assoc.has_many :profiles, -> { where(active: true) }
      end
    end

It was happening because the `option_merger` was taking the last
argument and checking if it was a Hash. This breaks the HasMany usage,
because its last argument can be a Hash or a Proc.

As the behavior described in this test:
https://github.com/rails/rails/blob/master/activesupport/test/option_merger_test.rb#L69
the method will only accept the lambda, this way it will keep the expected behavior. See 9eaa0a34

1 files changed, 2 insertions, 0 deletions

diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index b44e72a67c..a9c4980283 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -638,6 +638,8 @@ ActiveRecord::Schema.define do
 
   create_table :students, force: true do |t|
     t.string :name
+    t.boolean :active
+    t.integer :college_id
   end
 
   create_table :subscribers, force: true, id: false do |t|