Merge pull request spatie#75 from mvdnbrk/patch-1

Change static to self

Author: brendt

src/State.php

@@ -110,7 +110,7 @@ public static function resolveStateClass($state): ?string
             return get_class($state);
         }
 
-        foreach (static::resolveStateMapping() as $stateClass) {
+        foreach (self::resolveStateMapping() as $stateClass) {
             if (! class_exists($stateClass)) {
                 continue;
             }