fix: improve date format error message in ViewAppointmentByDateParser

Author: mervyn-teo

src/main/java/seedu/address/logic/parser/ViewAppointmentByDateParser.java

@@ -15,6 +15,9 @@
  */
 public class ViewAppointmentByDateParser implements Parser<ViewAppointmentByDateCommand> {
 
+    private static final String MESSAGE_INVALID_DATE_FORMAT =
+            "Please enter a valid date. The correct format is dd-MM-yyyy";
+
     @Override
     public ViewAppointmentByDateCommand parse(String args) throws ParseException {
         ArgumentMultimap argMultimap = ArgumentTokenizer.tokenize(args, PREFIX_DATE);
@@ -29,7 +32,7 @@ public ViewAppointmentByDateCommand parse(String args) throws ParseException {
         try {
             date = LocalDate.parse(argMultimap.getValue(PREFIX_DATE).get(), DateUtil.getDateFormatter());
         } catch (Exception e) {
-            throw new ParseException(String.format(MESSAGE_INVALID_COMMAND_FORMAT,
+            throw new ParseException(String.format(MESSAGE_INVALID_DATE_FORMAT,
                     ViewAppointmentByDateCommand.MESSAGE_USAGE));
         }