Japanese post code validation

Set Japanese post code validation.
Please check following site.
https://en.wikipedia.org/wiki/Postal_codes_in_Japan

includes/class-wc-validation.php

@@ -67,6 +67,9 @@ class WC_Validation {
 			case 'GB' :
 				$valid = self::is_GB_postcode( $postcode );
 				break;
+			case 'JP' :
+				$valid = (bool) preg_match( '/^\d{3}\-\d{4}$/', $postcode );
+				break;
 			case 'PT' :
 				$valid = (bool) preg_match( '/^([0-9]{4})([-])([0-9]{3})$/', $postcode );
 				break;