fix admin en_US file

apps/app/public/static/locales/en_US/admin.json

@@ -477,7 +477,7 @@
       "select_search_scope_children_as_default": "Select 'Only children of this tree' as default value of search range",
       "select_search_scope_children_as_default_desc": "When the setting value is off, 'All pages' is used as default value of search range.",
       "enable_marp": "Enable Marp ",
-      "enable_marp_desc": "When the setting value if off、you cannot use Marp。",
+      "enable_marp_desc": "When the setting value is off, you cannot use Marp.",
       "marp_official_site": "The Marp Official Site: ",
       "marp_official_site_link": "https://marp.app",
       "marp_in_growi" : "How to use Marp in GROWI: ",