Update release script to use trunk instead of master

[MAILPOET-3466]

mailpoet/RoboFile.php

@@ -745,10 +745,10 @@ class RoboFile extends \Robo\Tasks {
       $this->yell('Please make sure your working directory is clean before running release.', 40, 'red');
       exit(1);
     }
-    // checkout master and pull from remote
+    // checkout trunk and pull from remote
     $this->taskGitStack()
       ->stopOnFail()
-      ->checkout('master')
+      ->checkout('trunk')
       ->exec('git pull --ff-only')
       ->run();
     // make sure release branch doesn't exist on github

mailpoet/tasks/release/GitHubController.php

@@ -44,7 +44,7 @@ class GitHubController {
       'json' => [
         'title' => 'Release ' . $version,
         'head' => self::RELEASE_SOURCE_BRANCH,
-        'base' => 'master',
+        'base' => 'trunk',
       ],
     ]);
     $response = json_decode($response->getBody()->getContents(), true);
@@ -69,7 +69,7 @@ class GitHubController {
       'query' => [
         'state' => 'all',
         'head' => self::RELEASE_SOURCE_BRANCH,
-        'base' => 'master',
+        'base' => 'trunk',
         'direction' => 'desc',
       ],
     ]);