Add protection of stubbed methods from being called within a db transaction

[nepalez]

Use the within_transaction: false for the protection:

---
- class: GoogleTranslateDiff
- chain: translate
- within_transaction: false
- arguments:
    - Color
    - :from: en
      :to:   de
- actions:
    - return: Farbe

This method will raise an exception if the method is executed in a transaction:

GoogleTranslateDiff.translate "Color", from: "en", to: "de"
# => "Farbe"  

# but not within a transaction
ActiveRecord::Base.transaction do
  GoogleTranslateDiff.translate "Color", from: "en", to: "de"
  # => raise #<Isolator::UnsafeOperationError ...>
end