Fix missing Example::__toString method

This method is required by the Tag interface.

src/DocBlock/Tags/Example.php

@@ -134,6 +134,16 @@ final class Example extends BaseTag
         return $this;
     }
 
+    /**
+     * Returns a string representation for this tag.
+     *
+     * @return string
+     */
+    public function __toString()
+    {
+        return $this->filePath . ($this->description ? ' ' . $this->description->render() : '');
+    }
+
     /**
      * Returns true if the provided URI is relative or contains a complete scheme (and thus is absolute).
      *