tweak .travis.yml

.gitignore

@@ -1,3 +1,8 @@
+.Renviron
+.Rproj.user
+.Rhistory
+.RData
+*.Rproj
 README.html
 /inst/doc/*.log
 /vignettes/*.log

.travis.yml

@@ -1,6 +1,19 @@
 language: r
 sudo: false
 cache: packages
+matrix:
+  include:
+    - os: linux
+      r: oldrel
+    - os: linux
+      r: release
+    - os: linux
+      r: devel
+    - os: linux
+      dist: trusty
+      env: R_CODECOV=true
+    - os: osx
+      osx_image: xcode8.3
 r_packages:
 - covr
 - AER
@@ -40,4 +53,4 @@ r_packages:
 - truncreg
 - VGAM
 after_success:
-- Rscript -e 'library("covr");codecov()'
+- R -q -e 'library("covr");codecov()'