Raised PHP requirement to 7.1 and updated types.

Fixes #25

src/Event/Hook_Event_Config_Interface.php

@@ -1,11 +1,15 @@
 <?php
+declare( strict_types=1 );
 
 namespace Rarst\Laps\Event;
 
+/**
+ * Interface to retrieve configuration array of hook events to track.
+ */
 interface Hook_Event_Config_Interface {
 
 	/**
 	 * @return array
 	 */
-	public function get_events();
+	public function get_events(): array;
 }