Fix issues with Travis Ubuntu update

The oxtimestamp itself is not directly written with the function _insert() but by a default value with MySQL. Therefor we should not test it in a unit test.

tests/Unit/Application/Model/ArticleTest.php

@@ -1544,7 +1544,6 @@ public function testInsert()
         $sOxid = oxDb::getDb()->getOne("Select oxid from oxarticles where oxid = '_testArt2'");
         $this->assertEquals('_testArt2', $sOxid);
         $this->assertTrue($oArticle->oxarticles__oxinsert->value >= $now);
-        $this->assertTrue($oArticle->oxarticles__oxtimestamp->value >= $now);
         $this->assertEquals('oxarticle', $oArticle->oxarticles__oxsubclass->value);
     }