Merge branch 'feature/drone-pipeline'

.drone.yml

@@ -7,6 +7,18 @@ steps:
 - name: lintr
   image: jupyter/datascience-notebook
   commands:
+  - export TAR="/bin/tar"
   - Rscript -e 'devtools::install_github("jimhester/lintr")'
-                  - Rscript -e 'lintr::lint_package()'
-
+  # Lint the document, printing output.
+  - |
+    Rscript -e 'lintr::lint_dir(
+      path=".", pattern=rex::rex(".", one_of("Rr"), maybe("md"), end)
+    )'
+  # Return non-zero exit code (no output is printed).
+  - |
+    Rscript -e 'quit(
+      save="no",
+      status=length(
+        lintr::lint_dir(path=".", pattern=rex::rex(".", one_of("Rr"), maybe("md"), end))
+      )
+    )'