catch not ready to migrate exceptions

.travis.yml

@@ -1,8 +1,6 @@
 language: php
 php:
-  - 5.5
   - 5.6
-  - hhvm
   - 7
 script:
   - phpunit -c tests/phpunit.xml --coverage-clover=coverage.clover

src/Collection.php

@@ -103,6 +103,8 @@ public function migrate($direction = MigrationInterface::DIRECTION_UP)
                 $result->attach($item);
             } catch (AlreadyMigratedException $e) {
                 /** we will not execute migrations that are already executed */
+            } catch (NotReadyToMigrateException $e) {
+                /** we will not execute migrations that are not ready to be executed */
             }
         }
 

src/NotReadyToMigrateException.php

@@ -0,0 +1,12 @@
+<?php
+namespace Genkgo\Migrations;
+
+use RuntimeException;
+
+/**
+ * Class NotReadyToMigrateException
+ * @package Genkgo\Migrations
+ */
+class NotReadyToMigrateException extends RuntimeException
+{
+}