fix: specify the return value type

Co-authored-by: Progi1984 <progi1984@gmail.com>

Author: jnlin

src/PhpWord/PhpWord.php

@@ -261,7 +261,7 @@ public function setDefaultFontName($fontName): void
      *
      * @return string
      */
-    public function getDefaultAsianFontName()
+    public function getDefaultAsianFontName(): string
     {
         return Settings::getDefaultAsianFontName();
     }