Bump postgres version in travis.

3.10 requires pg 9.6

.travis.yml

@@ -1,7 +1,7 @@
 language: php
 
 addons:
-  postgresql: "9.5"
+  postgresql: "9.6"
 
 services:
   - mysql
@@ -30,7 +30,7 @@ before_install:
   - nvm install 14.0.0
   - nvm use 14.0.0
   - cd ../..
-  - composer create-project -n --no-dev --prefer-dist moodlehq/moodle-plugin-ci ci dev-master
+  - composer create-project -n --no-dev --prefer-dist moodlehq/moodle-plugin-ci ci ^3
   - export PATH="$(cd ci/bin; pwd):$(cd ci/vendor/bin; pwd):$PATH"
 
 install: