Update postal codes to new 5 digit format

[ReedJessen]

As of August 1st, 2015, the Korean postal code system has be overhauled to a 5 digit system rather than the 6 digit system represented in this data. The data in this repo is out of date.

Should updated to reflect new standard.

Explication of new standard: https://en.wikipedia.org/wiki/List_of_postal_codes_in_South_Korea

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[seiwonpark]

@ReedJessen If you need the data still, you can download it from business.juso.go.kr. They provide not only korean road names, postal codes, but also in english. I hope this will help.