Travis CI: Update to bionic, add new PostgreSQL versions

.travis.yml

@@ -1,22 +1,21 @@
-dist: xenial
+dist: bionic
 language: c
 addons:
   apt:
     sources:
-      - sourceline: 'deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main'
+      - sourceline: 'deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main'
         key_url: 'https://www.postgresql.org/media/keys/ACCC4CF8.asc'
     update: true
     packages:
       - liburiparser-dev
 env:
-  - PGVERSION=9.1
-  - PGVERSION=9.2
   - PGVERSION=9.3
   - PGVERSION=9.4
   - PGVERSION=9.5
   - PGVERSION=9.6
   - PGVERSION=10
   - PGVERSION=11
+  - PGVERSION=12
 script: |
   set -e
   PATH=/usr/lib/postgresql/$PGVERSION/bin:$PATH