lang: make "OK" capitalization consistent

lang/main.json

         "muteParticipantButton": "Mute",
         "muteParticipantDialog": "Are you sure you want to mute this participant? You won't be able to unmute them, but they can unmute themselves at any time.",
         "muteParticipantTitle": "Mute this participant?",
-        "Ok": "Ok",
+        "Ok": "OK",
         "passwordLabel": "The meeting has been locked by a participant. Please enter the $t(lockRoomPassword) to join.",
         "passwordNotSupported": "Setting a meeting $t(lockRoomPassword) is not supported.",
         "passwordNotSupportedTitle": "$t(lockRoomPasswordUppercase) not supported",