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, 1 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/option_merger.rb b/activesupport/lib/active_support/option_merger.rb
index e55ffd12c3..dea84e437f 100644
--- a/activesupport/lib/active_support/option_merger.rb
+++ b/activesupport/lib/active_support/option_merger.rb
@@ -12,7 +12,7 @@ module ActiveSupport
 
     private
       def method_missing(method, *arguments, &block)
-        if arguments.last.is_a?(Proc)
+        if arguments.first.is_a?(Proc)
           proc = arguments.pop
           arguments << lambda { |*args| @options.deep_merge(proc.call(*args)) }
         else