modify .travis.yml to make travis-ci work (add dist:trusty)
diff --git a/.travis.yml b/.travis.yml
index 0d7d2a6..49be497 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,3 +1,5 @@
+dist: trusty
+
 notifications:
   email:
     recipients: