Travis is actually running trusty. xenial isn't supported yet.

tannewt · tannewt · commit 6c858c7a7867 · 2017-01-12T17:09:10.000-08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 sudo: required
-dist: xenial
+dist: trusty
 language: c
 compiler:
   - gcc
