Fix CI failures (#4046)

Author: yutannihilation

.github/workflows/R-CMD-check.yaml

@@ -10,7 +10,7 @@ name: R-CMD-check
 
 # Increment this version when we want to clear cache
 env:
-  cache-version: v1
+  cache-version: v2
 
 jobs:
   R-CMD-check:
@@ -77,6 +77,11 @@ jobs:
           sysreqs=$(Rscript -e "cat(sysreqs::sysreq_commands('DESCRIPTION'))")
           sudo -s eval "$sysreqs"
 
+      # Remove this when the new rmarkdown is released on CRAN
+      - name: "Workaround for rstudio/rmarkdown#1831"
+        if: runner.os == 'Linux' && matrix.config.r < '3.6'
+        run: Rscript -e "remotes::install_github('rstudio/rmarkdown')"
+
       - name: Install system dependencies on macOS
         if: runner.os == 'macOS'
         run: |

.travis.yml

@@ -26,6 +26,9 @@ env:
   # switch off vdiffr by default
   - VDIFFR_RUN_TESTS=false
 
+# Workaround for rstudio/rmarkdown#1831
+r_github_packages: rstudio/rmarkdown
+
 after_success:
   - Rscript -e 'covr::codecov()'