Fix after zeitwerkify

[kzaitsev]

Since dry-monads was switched to zeitwerk it seems brokes constant name resolving.

This minor patch fixes the initialization issue:

An error occurred while loading spec_helper.
Failure/Error: require "dry/monads/result"

NameError:
  uninitialized constant Dry::Monads::Result::Transformer
# ./lib/dry/transaction.rb:3:in `require'
# ./lib/dry/transaction.rb:3:in `<top (required)>'
# ./lib/dry-transaction.rb:3:in `require'
# ./lib/dry-transaction.rb:3:in `<top (required)>'
# ./spec/spec_helper.rb:11:in `require'
# ./spec/spec_helper.rb:11:in `<top (required)>'
No examples found.