changing new test to allow running on php 5.3

Author: Peter Lind

tests/PhpPresentation/Tests/Writer/AbstractWriterTest.php

@@ -51,7 +51,8 @@ public function testAllDrawingsIncludesMasterSlides()
         $activeSlide = $presentation->getActiveSlide();
         $activeSlide->createDrawingShape();
 
-        $masterSlide = $presentation->getAllMasterSlides()[0];
+        $masterSlides = $presentation->getAllMasterSlides();
+        $masterSlide = $masterSlides[0];
         $masterSlide->createDrawingShape();
 
         $writer = $this->getMockForAbstractClass('PhpOffice\\PhpPresentation\\Tests\\Writer\\AbstractWriter');