Switched CI to use the conda plugin

[jenzopr]

The new conda plugin for buildkite is finally working. It takes care of all conda related stuff and executes the pipeline's step command within the environment specified by .buildkite/environment.yml.

[HendrikSchultheis]

Looks good to me.
But with #22 there are two more packages added with the suggests tag (knitr & rmarkdown). Also now that there are vignettes devtools needs qpdf to check for pdf compression.

[jenzopr]

@HendrikSchultheis the dependencies qpdf and vdiffr are now available from conda-forge and were installed in the wilson environment.
However, the R CMD CHECK failed:

checking tests ...
Running ‘testthat.R’ [21s/25s]
ERROR
Running the tests in ‘tests/testthat.R’ failed.
Last 13 lines of output:
Unable to change to a locale which provides the desired dec. You will need to add a valid locale name to getOption("datatable.fread.dec.locale"). See the long paragraph in ?fread. Run again with verbose=TRUE to inspect.
1: parser(file = "wiki_example.clarion", dec = ",") at testthat/test-parser.R:4
2: data.table::fread(input = file, fill = TRUE, header = FALSE, dec = dec, nrows = num_header, integer64 = "double")
3: stop("Unable to change to a locale which provides the desired dec. You will need to add a valid locale name to getOption(\"datatable.fread.dec.locale\"). See the long paragraph in ?fread.", if (verbose) "" else " Run again with verbose=TRUE to inspect.")
 
══ testthat results  ═══════════════════════════════════════════════════════════
OK: 52 SKIPPED: 2 FAILED: 3
1. Error: ggplot is downloadable (@test-download.R#11)
2. Error: complexHeatmap is downloadable (@test-download.R#37)
3. Error: file is parsed correctly (@test-parser.R#4)
 
Error: testthat unit tests failed
Execution halted

[HendrikSchultheis]

This is fixed by adding the french locale (fr_FR.utf8) via dpkg-reconfigure locales which is the default locale for "," decimal separators in the data.table package.

[HendrikSchultheis]

Sadly the tests are still failing because of r-base being not capable of using png. See here.