Fix UnicodeDecodeError for Chinese

[Brightcells]

ipdb> value
'\xe8\xa5\xbf\xe6\xb1\x89\xe6\x96\x87\xe5\xad\xa6\xe6\x88\x90\xe5\xb0\xb1\xe4\xb8\xad\xef\xbc\x8c\xe6\x9c\x80\xe4\xb8\xba\xe7\xaa\x81\xe5\x87\xba\xe7\x9a\x84\xe6\x98\xaf\xef\xbc\x9f'
ipdb> unicode(value)
*** UnicodeDecodeError: 'ascii' codec can't decode byte 0xe8 in position 0: ordinal not in range(128)
ipdb> cc.Convert2Unicode(value)

u'\u897f\u6c49\u6587\u5b66\u6210\u5c31\u4e2d\uff0c\u6700\u4e3a\u7a81\u51fa\u7684\u662f\uff1f'
ipdb> print cc.Convert2Unicode(value)

西汉文学成就中，最为突出的是？
ipdb>

[Parkayun]

@Brightcells
Hi. Can I know why use CodeConvert instead of to write function?
I want this package has minimum dependency.
And test failed.

[Brightcells]

Chinese character may be utf8 or gbk.
I does not to test whether Chinese character in .bson file can be gbk or not.
Instead I use CodeConvert to realize convert to unicode.

[Brightcells]

Fixed travis tests