Fixed PHP 5.6 incompatibilities

Author: remorhaz

src/Pointer/Evaluate/AdvancerIndex.php

@@ -14,12 +14,13 @@ public function canAdvance()
 
     public function advance()
     {
-        $data = &$this
+        $cursorData = &$this
             ->getCursor()
-            ->getData()[$this->getKey()];
+            ->getData();
+        $cursorData = &$cursorData[$this->getKey()];
         $this
             ->getCursor()
-            ->setData($data);
+            ->setData($cursorData);
         return $this;
     }
 

src/Pointer/Evaluate/AdvancerProperty.php

@@ -14,13 +14,13 @@ public function canAdvance()
 
     public function advance()
     {
-        $data = &$this
+        $cursorData = &$this
             ->getCursor()
-            ->getData()
-            ->{$this->getKey()};
+            ->getData();
+        $cursorData = &$cursorData->{$this->getKey()};
         $this
             ->getCursor()
-            ->setData($data);
+            ->setData($cursorData);
         return $this;
     }