Adding Japanese postal code format

Very straightforward. Japanese postal codes consist of 7 digits, optionally separating the first three digits from the last four with a hyphen . [Data from Google](http://i18napis.appspot.com/address/data/JP). 

__Proposed format__
`^\d{3}-?\d{4}$$`

__Examples__
- 154-0023
- 350-1106