switch to trusty (#352)

mllg · jakob-r · commit 655591e12882 · 2018-03-27T10:32:54.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,5 @@
 language: r
+dist: trusty
 sudo: false
 cache: packages
 r:
