thai_strftime: %O modifier failed to convert year to Thai digit

[bact]

O (capital Oh) modifier in thai_strftime() failed to convert %y and %Y to alternative numeric symbols (Thai digit).

Code: thai_strftime(datetime.datetime(1976, 10, 6, 1, 40), "%Od %Ob %Oy")
Expect: '๐๖ ต.ค. ๒๕๑๙'
Actual: '๐๖ ต.ค. 2519'

[wannaphong]

I found same bug on Windows 10. Python 3.7.6

>>> from pythainlp.util import thai_strftime
>>> import datetime
>>> thai_strftime(datetime.datetime(1976, 10, 6, 1, 40), "%Od %Ob %Oy")
'๐๖ ต.ค. 19'