Check R-release, clang only as a default.

paulnorthrop · paulnorthrop · commit 9abd843481af · 2017-05-31T19:22:36.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -23,7 +23,7 @@ addons:
 
 r:
   - release
-  - devel
+#  - devel
 #  - oldrel
 
 env:
