Log Message:
(math/R-gstat) Updated 2.0.9 to 2.1.1 (NEWS.md is not fully updated)

# version 2.1-0

* import `sftime`; modify `krigeST()` variogram functions to accept
  `sftime` objects for `data` (as alternative to `STI` or `STIDF`),
  and `stars` or `sftime` objects for `newdata`; #108 with great help
  from @henningte

* fix Gaussian cosimulation, probably introduced in 2016, #106