Strange trend line on line graphs

Hi, after working with C3 for some months I found the following issue.

Some graphs display a trendline when I try to print this graphs from the browser. I don't know if its and issue with C3 or maybe a browser related issue.


Any ideas are received.

thanks

You can use the following data to test this.

[test_data.json.zip](https://github.com/c3js/c3/files/863076/test_data.json.zip)

Start by reproducing the reported trend line with the attached test_data.json.zip, the example image, and the browser's print workflow. Compare the printed graph with the on-screen graph across browsers to determine whether the behavior is in C3 or browser rendering. Done means the cause is isolated and a reproducible fix or supported limitation is documented.

Written by the indexing model from the issue text.