Use getLineNo() not getLineNumber() as replacement for property access

This will ensure unchanged behaviour.
`getLineNumber()` will return `null` instead of `0`.

Author: JakeQZ

src/RuleSet/DeclarationBlock.php

@@ -434,8 +434,8 @@ public function expandBackgroundShorthand()
             'background-repeat' => ['repeat'],
             'background-attachment' => ['scroll'],
             'background-position' => [
-                new Size(0, '%', false, $this->getLineNumber()),
-                new Size(0, '%', false, $this->getLineNumber()),
+                new Size(0, '%', false, $this->getLineNo()),
+                new Size(0, '%', false, $this->getLineNo()),
             ],
         ];
         $mRuleValue = $oRule->getValue();
@@ -801,7 +801,7 @@ public function createFontShorthand()
                 $aLHValues = $mRuleValue->getListComponents();
             }
             if ($aLHValues[0] !== 'normal') {
-                $val = new RuleValueList('/', $this->getLineNumber());
+                $val = new RuleValueList('/', $this->getLineNo());
                 $val->addListComponent($aFSValues[0]);
                 $val->addListComponent($aLHValues[0]);
                 $oNewRule->addValue($val);
@@ -817,7 +817,7 @@ public function createFontShorthand()
         } else {
             $aFFValues = $mRuleValue->getListComponents();
         }
-        $oFFValue = new RuleValueList(',', $this->getLineNumber());
+        $oFFValue = new RuleValueList(',', $this->getLineNo());
         $oFFValue->setListComponents($aFFValues);
         $oNewRule->addValue($oFFValue);