(devel/R-usethis) Updated 2.1.5 to 2.1.6

# usethis 2.1.6

### GitHub-related

`use_github_action()` and friends gain a `ref` argument, which
defaults to the tag of the latest release in
<https://github.com/r-lib/actions> (#1541).

`use_github_actions_badge()` now uses the same URLs as GitHub does via
the "Create status badge" helper in the browser (#1525). This changes
the significance of the `name` argument; now it really must be the
name of the workflow configuration file.

All functions error more clearly when the requested operation is not
supported for the "theirs" remote configuration (#1588).

### Other changes

`use_roxygen_md()` gains an `overwrite` argument (#1599).

`use_rscloud_badge()` is a new function that creates a README badge
indicating the repository can be launched in an [RStudio
Cloud](https://rstudio.cloud) project (@gvelasq, #1584).

`use_data()` gains an `ascii` argument, which is passed along to
`save()` (@JosiahParry, #1625).

`use_code_of_conduct()` has been updated to version 2.1 of the
Contributor Covenant (@batpigandme, #1591).

(mef)