Clone detection paper from SANER 2019

Add “Learning-Based Recursive Aggregation of Abstract Syntax Trees for Code Clone Detection” paper

Please fill the [ ] with an x to make sure that you read and followed the checklist

[x] This addition is about Machine Learning on Code specifically. General links should be added to Awesome Machine Learning instead.
[x] I have checked that the proposed addition is not already in the awesome list.
[x] I have signed-off my commits as detailed here.

[x] The links follow the link template:

* [Title](URL) - Description.

* [Title](URL) - Description [Code](link to code).

[x] The addition is correctly classified as a paper, blog post, talk, software or dataset.
[x] The commit message must start with a verb (Add …, Deprecate …) and end without a dot. For exemple:
```
Deprecate Theano software
```

src-d / awesome-machine-learning-on-source-code