Remove use of PHP language features incompatible with 5.6

Author: JakeQZ

src/CSSList/CSSBlockList.php

@@ -71,7 +71,7 @@ protected function allRuleSets(array &$aResult)
      *
      * @see RuleSet->getRules()
      */
-    public function getAllValues($element = null, bool $searchInFunctionArguments = false): array
+    public function getAllValues($element = null, $searchInFunctionArguments = false)
     {
         $searchString = null;
         if ($element === null) {

tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php

@@ -9,12 +9,20 @@
 
 final class ConcreteCSSBlockList extends CSSBlockList
 {
-    public function isRootList(): bool
+    /**
+     * @return never
+     */
+    public function isRootList()
     {
         throw new \BadMethodCallException('Not implemented', 1740395831);
     }
 
-    public function render(OutputFormat $outputFormat): string
+    /**
+     * @param OutputFormat|null $outputFormat
+     *
+     * @return never
+     */
+    public function render($outputFormat)
     {
         throw new \BadMethodCallException('Not implemented', 1740395836);
     }