save_image not working under windows #2483

Hi, I tried to use save_image under windows but got hit with an error message about unable to decode unicode bytes.

It traced back to plotly.R/R/kaleido.R where reticulate::py_run_string is called, causing it to try to open something with C:\users in its path. string to interpret \u as unicode escaping and it fails.

A few lines before that there is a tmp_json <- tempfile(fileext = ".json" ) and I think that this creates the wrong path part. Possibly the easiest solution here would be to replace the backslash with a forward slash as python can understand those on all platforms.