add the chinese ref in place to tackle the memory issue
# What does this PR do?

@wlhgtc 
It eats my 200+GB memory when adding the chinese refs, OOM killed, can't go further.
My train corpus has 17067704 lines (size: 1GB)

datasets 1.6.2 come with a new in-place add_column function, which saves the heavy coping.
Both two ways work well on my own process, but `add_columns` is 4x faster than the original method.
![CleanShot 2021-05-13 at 10 19 22@2x](https://user-images.githubusercontent.com/16603773/118068382-da30c500-b3d4-11eb-8a74-f169593a482b.png)
LGTM!<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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