build(travis): update env & deps

Author: mydearxym

.travis.yml

@@ -1,10 +1,10 @@
 language: elixir
 elixir:
-  - 1.8
+  - 1.9
 otp_release:
   - 21.0
 addons:
-  postgresql: '9.4'
+  postgresql: '9.6'
 
 before_install:
   - sudo chown -R travis ./travis/install_node.sh