Cast return values of lowest and highest methods to string

Author: tangrufus

src/Versions.php

@@ -25,13 +25,13 @@ public static function lowest(string ...$versions): string
     {
         $sorted = self::sort(...$versions);
 
-        return array_first($sorted);
+        return (string) array_first($sorted);
     }
 
     public static function highest(string ...$versions): string
     {
         $sorted = self::sort(...$versions);
 
-        return array_last($sorted);
+        return (string) array_last($sorted);
     }
 }