Add missing iterator return type-hint (#44)

Mapping/MappingCollection.php

@@ -2,8 +2,6 @@
 
 namespace SofaScore\Purgatory\Mapping;
 
-use Traversable;
-
 class MappingCollection implements \IteratorAggregate, \Countable
 {
     /**
@@ -12,29 +10,15 @@ class MappingCollection implements \IteratorAggregate, \Countable
     protected array $mappings = [];
 
     /**
-     * (PHP 5 &gt;= 5.0.0)<br/>
-     * Retrieve an external iterator.
-     *
-     * @see http://php.net/manual/en/iteratoraggregate.getiterator.php
-     *
-     * @return Traversable An instance of an object implementing <b>Iterator</b> or
-     *                     <b>Traversable</b>
+     * {@inheritdoc}
      */
-    public function getIterator()
+    public function getIterator(): \Traversable
     {
         return new \ArrayIterator($this->mappings);
     }
 
     /**
-     * (PHP 5 &gt;= 5.1.0)<br/>
-     * Count elements of an object.
-     *
-     * @see http://php.net/manual/en/countable.count.php
-     *
-     * @return int The custom count as an integer.
-     *             </p>
-     *             <p>
-     *             The return value is cast to an integer.
+     * {@inheritdoc}
      */
     public function count(): int
     {