trying a newer linux distro in Travis

Hoping to fix an issue related to openssl, where 1.0.1 doesn't seem to work, but 1.0.2 does.

Author: dylemma

.travis.yml

@@ -1,7 +1,7 @@
 # Based on the "trust" template v0.1.1
 # https://github.com/japaric/trust/tree/v0.1.1
 
-dist: trusty
+dist: xenial
 language: rust
 services: docker
 sudo: required