(devel/R-covr) Updated 3.5.0 to 3.5.1, make test fails

# covr 3.5.1

* Generated files from [cpp11](https://cpp11.r-lib.org/) are now ignored (#437)

* `codecov()` and `coveralls()` now retry failed requests before raising an error (#428, @jameslamb)

(mef)