Update locale.constant-en_US.json

Since “Hangul(한글)” means letters, the expression “Korean(한국어)” is more appropriate.

@@ -2482,7 +2482,7 @@
             "zh_TW": "繁體中文",
             "en_US": "English",
             "it_IT": "Italiano",
-            "ko_KR": "한글",
+            "ko_KR": "한국어",
             "ru_RU": "Русский",
             "es_ES": "Español",
             "ja_JA": "日本語",