fix: fix to save the categorical values with type casting

[koseoyoung]

works on #18

Previously it has such error:

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 [Unable to show a serialized python object.]]

The root cause of this issue is that np.save requires np data type, which is str when we save the generated cat file (which contains string value) into the disk. I fixed it through this PR. #19

After this fix:

[['Spain', '1', '1', '0'],
 ['Germany', '0', '1', '0'],
 ['Germany', '0', '1', '0'],
 ['Germany', '1', '1', '0'],
 ['Germany', '1', '0', '0'],
 ['Spain', '0', '1', '1'],
 ['Spain', '1', '0', '0'],
 ['Germany', '0', '1', '1'],
 ['Spain', '0', '1', '0'],
 ['Spain', '1', '1', '0'],
 ['Spain', '1', '1', '0'],
 ['France', '1', '0', '0'],
 ['Germany', '1', '1', '0'],
 ['Germany', '0', '1', '0'],
 ['Spain', '0', '0', '1'],
 ['France', '1', '0', '0'],
 ['France', '0', '1', '1'],
 ['Spain', '1', '1', '0'],
 ['Spain', '1', '1', '0'],
 ['France', '0', '0', '1'],
 ['France', '0', '1', '0'],
 ['Spain', '0', '1', '0'],
 ['Germany', '0', '1', '0'],