More errors during tests on CRAN

[kadyb]

 ── FAILURE (test-minmaxDTM_get.R:35:3): check if results are equal ─────────────
  `minmax` not equal to suppressWarnings(minmaxDTM_get(polygon_4326)).
  Component "elev": Mean relative difference: 14.64775
  Component "geom": Attributes: < Component "bbox": Mean relative difference: 1 >
  Component "geom": Component 1: Mean relative difference: 1
  Component "geom": Component 2: Mean relative difference: 1

Warning (test-pointDTM_get.R:5:1): (code run outside of `test_that()`)

  -- ERROR (test-tile_download.R:13:1): (code run outside of `test_that()`) ------
  Error: non-character argument
  Backtrace:
      x
   1. \-rgugik::tile_download(orto, outdir = tmp) test-tile_download.R:13:0
   2. +-base::unlist(strsplit(df_req[1, "URL"], "/"))
   3. \-base::strsplit(df_req[1, "URL"], "/")

[kadyb]

Fixed in #54.