change null->void in hook return type

CHANGELOG.md

+## [1.4.1] - 2019-11-19
+### Fixed
+- Invalid return type in Hookable interface
+
 ## [1.4.0] - 2019-09-26
 ### Added
 - SlimPlugin - abstract class with only most important plugin elements

src/Plugin/Hookable.php

@@ -7,7 +7,7 @@ interface Hookable {
 	/**
 	 * Init hooks (actions and filters).
 	 *
-	 * @return null
+	 * @return void
 	 */
 	public function hooks();