enhance day validation regex for date format

[GavinChenYan]

“inputDate”: “2017-13-25",
error is
{ “error” : {“statusCode”:400,“code”:“ERR11004",“message”:“VALIDATOR_SCHEMA”,“description”:“Schema Validation Error - $.inputDate: does not match the date pattern ^\d{4}-(?:0[0-9]{1}|1[0-2]{1})-[0-9]{2}$“} }

so, months validation is correct

for days we have this
“inputDate”: “2017-12-35",
java.time.format.DateTimeParseException: Text ‘2017-12-35’ could not be parsed: Invalid value for DayOfMonth (valid values 1 - 28/31): 35
this is thrown in API code
so swagger allows invalid day
doesn’t allow invalid month

It should have similar validation error as incorrect month

[GavinChenYan]

changed the date-time format regex to fix the issue #65

[stevehu]

Looks really good. Thanks.