Swiftmailer 6.0 compatibility (#21)

* Clean up

* Updated phpunit

* Refactoring for v2

* Refectory for v2 pt2

* Required dev php7

Phpunit v6 requires php7 to run

* Fancy helpers

* Prioritise jobs in background

* Use temp arrays to prioritise jobs

* Coveralls

* Coverall config

* Adjusted waiting time on test

* Typo fix

* Removed deprecated flag

* Added Coverage badge to readme

* Removed psr/log suggestion

* Fixed typo in composer.json

* Fixes from styleci

* Downgraded phpunit

Using an older version of phpunit to allow testing on php5, as phpunit
v6 requires php7

* Added php 7.1 supported version

* More fixes from styleci

* Fixes from styleci

* Reordered badges + styleci badge

* Increased tests waiting time when testing file output

* Typo in the documentation

Ref #16

* Fix #20

Added support for SwiftMailer ^6.0

::newInstance() method has been deprecated, along with
Swift_MailTransport.

The default mail transport is now sendmail when using swiftmailer

https://legalhackers.com/advisories/SwiftMailer-Exploit-Remote-Code-Exec
-CVE-2016-10074-Vuln.html

composer.json

@@ -23,10 +23,10 @@
     "require-dev": {
         "phpunit/phpunit": "~5.7",
         "satooshi/php-coveralls": "^1.0",
-        "swiftmailer/swiftmailer": "~5.4"
+        "swiftmailer/swiftmailer": "~5.4 || ^6.0"
     },
     "suggest": {
-        "swiftmailer/swiftmailer": "Required to send the output of a job to email address/es (~5.4)."
+        "swiftmailer/swiftmailer": "Required to send the output of a job to email address/es (~5.4 || ^6.0)."
     },
     "autoload": {
         "psr-4": {

src/GO/Traits/Mailer.php

@@ -29,7 +29,7 @@ public function getEmailConfig()
         if (! isset($this->emailConfig['transport']) ||
             ! ($this->emailConfig['transport'] instanceof \Swift_Transport)
         ) {
-            $this->emailConfig['transport'] = \Swift_MailTransport::newInstance();
+            $this->emailConfig['transport'] = new \Swift_SendmailTransport();
         }
 
         return $this->emailConfig;
@@ -43,13 +43,11 @@ public function getEmailConfig()
      */
     private function sendToEmails(array $files)
     {
-        $mailer = \Swift_Mailer::newInstance(
-            $this->emailConfig['transport']
-        );
+        $mailer = new \Swift_Mailer($this->emailConfig['transport']);
 
         $config = $this->getEmailConfig();
 
-        $message = \Swift_Message::newInstance()
+        $message = (new \Swift_Message())
             ->setSubject($config['subject'])
             ->setFrom($config['from'])
             ->setTo($this->emailTo)