CI: include pyarrow 0.15.0 / latest release in one of the builds

[jorisvandenbossche]

From a quick look, it seems we are not testing the latest version of pyarrow on our CI.

[alimcmaster1]

Any particular build you suggest adding this to? Or are you thinking a new one? @jorisvandenbossche

[jorisvandenbossche]

@alimcmaster1 sorry, forgot to answer here. I don't have a particular one in mind (but probably we need conda-forge for a recent version, which might complicate things). Looking into this now.