Update CI versions (brianc#88)

* Update CI versions

PostgreSQL 9.1 is no longer available on 14.04.

* Add Node 9 to CI

Author: charmander

.travis.yml

@@ -5,6 +5,13 @@ matrix:
     - node_js: "4"
       addons:
         postgresql: "9.1"
+      dist: precise
     - node_js: "6"
       addons:
         postgresql: "9.4"
+    - node_js: "8"
+      addons:
+        postgresql: "9.6"
+    - node_js: "9"
+      addons:
+        postgresql: "9.6"