Use better regex for finding translations in files in extension:translations

[peterjaap]

See https://github.com/tzyganu/MagentoTranslationTool/blob/master/app/code/community/Easylife/Translation/Model/Handler.php#L22

[peterjaap]

Or look to Magento 2's collect-phrases command for ideas; https://github.com/magento/magento2/blob/develop/setup/src/Magento/Setup/Console/Command/I18nCollectPhrasesCommand.php