update .travis.yml

Use @andysouth 's version from _rnaturalearth_ to get _sf_ to install properly

.travis.yml

@@ -1,8 +1,37 @@
 # R for travis: see documentation at https://docs.travis-ci.com/user/languages/r
 
-language: R
-sudo: false
+# .travis.yml
+
+# from tigris
+
+# from Andy South (rnaturalearth's travis.yml to build sf)
+language: r
+warnings_are_errors: true
+sudo: required
 cache: packages
 
+matrix:
+    include:
+        - os: linux
+          r: release
+          dist: trusty # 14.04
+          env: R_CODECOV=true
+        - os: linux
+          r: devel
+          dist: trusty
+
+before_install:
+    - sudo add-apt-repository ppa:ubuntugis/ubuntugis-unstable --yes
+    - sudo apt-get --yes --force-yes update -qq
+    - sudo apt-get install --yes udunits-bin libproj-dev libgeos-dev libgdal-dev libgdal1-dev libudunits2-dev
+
+notifications:
+  email:
+    on_success: change
+    on_failure: change
+
+r_github_packages:
+      - jimhester/covr
+
 after_success:
-  - Rscript -e 'covr::codecov()'
+      - Rscript -e 'covr::codecov()'