Libraries can not be detected

I installed the modue following this instruction.
- download module mailgun
- download libraries at https://github.com/mailgun/mailgun-php/tree/v1.7.2
- Extract the downloaded module in folder sites/all/libraries folder sẽ như thế này sites/all/libraries/mailgun.
- Enable module. Goto config admin/config/system/mailgun
- There comes the message "The Mailgun PHP library is not installed. Please see documentation for more information." then could not save api key.
- After checking, I see that the problem comes from declaring libraries

'version arguments' => array(
      'file' => 'vendor/mailgun/mailgun-php/src/Mailgun/Constants/Constants.php',
      // const SDK_VERSION = "1.7";
      'pattern' => '/const SDK_VERSION = \"((\d+)\.(\d+))\";/',
    ),

- The file path is incorrect. The code needs to be changed to:

'version arguments' => array(
      'file' => 'src/Mailgun/Constants/Constants.php',
      // const SDK_VERSION = "1.7";
      'pattern' => '/const SDK_VERSION = \"((\d+)\.(\d+))\";/',
    ),

so that libraries can be detected. Or just download at Mailgun libraries