sample.R fails with integer metadata

[gwaybio]

The error I receive:

Error in bind_rows_(x, .id) :
  Column `Metadata_diff_day` can't be converted from integer to character
 Calls: %>% ... withVisible -> <Anonymous> -> bind_rows -> bind_rows_ -> .Call
 Execution halted

The code causing the problems:

https://github.com/broadinstitute/cytominer_scripts/blob/master/sample.R#L80-L82

How to fix

I think all metadata columns should be coerced into characters. I will try and file a PR