Set explicit visibility on class constants

src/MDPhoneTypesSet.php

@@ -17,9 +17,9 @@
  */
 final class MDPhoneTypesSet extends MDValueSet {
 
-    const DEFAULT_PHONE_TYPE = 'work';
+    public const DEFAULT_PHONE_TYPE = 'work';
 
-    const PHONE_TYPES = [
+    public const PHONE_TYPES = [
         'work',
         'home',
         'mobile',