Improve .travis.yml to build the lesson

Author: rgaiacs

bin/boilerplate/.travis.yml

@@ -1,14 +1,23 @@
+# dist: trusty  # Ubuntu 14.04
 language: python
 python: 3.6
 branches:
   only:
   - gh-pages
   - /.*/
 before_install:
+  - sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9
+  - echo "deb https://cran.rstudio.com/bin/linux/ubuntu trusty/" | sudo tee -a /etc/apt/sources.list
+  - sudo apt-get update -y
+  - sudo apt-get install -y r-base
+  - sudo Rscript -e "install.packages('knitr', repos = 'https://', dependencies = TRUE)"
+  - sudo Rscript -e "install.packages('stringr', repos = 'https://cran.rstudio.com', dependencies = TRUE)"
+  - sudo Rscript -e "install.packages('checkpoint', repos = 'https://cran.rstudio.com', dependencies = TRUE)"
+  - sudo Rscript -e "install.packages('ggplot2', repos = 'https://cran.rstudio.com', dependencies = TRUE)"
   - rvm default
-  - gem install json kramdown
+  - gem install json kramdown jekyll
 install:
   - pip install pyyaml
 script:
-  - make lesson-check
   - make lesson-check-all
+  - make --always-make site