try to install postgresql-9.6-postgis-2.4 using sudo

.travis.yml

@@ -2,7 +2,7 @@ language: rust
 cache: cargo
 
 dist: trusty
-sudo: false
+sudo: required
 
 branches:
   except:
@@ -11,16 +11,19 @@ branches:
 services:
   - postgresql
 
-# addons:
-#   postgresql: 9.6
-#   apt:
-#     packages:
-#       - postgresql-9.6-postgis-2.4
+addons:
+  postgresql: 9.6
+  # apt:
+  #   packages:
+  #     - postgresql-9.6-postgis-2.4
 
 env:
   - DATABASE_URL=postgres://postgres@localhost/test
 
 before_script:
+  - sudo apt-get -qq update
+  - sudo apt-cache search postgis
+  - sudo apt-get install -y postgresql-9.6-postgis-2.4
   - psql -U postgres -c 'create database test'
   - psql -U postgres -d test -c 'create extension postgis'
   - psql -U postgres -d test -f fixtures/tilebbox.sql