Update .travis.yml to solve PostgreSQL issues with new base images

Travis CI updated the base images so the hacky PG 10 install is no
longer needed and on top of that is failing the builds.

Author: Alex-Vol-SV

.travis-postgres10.sh

@@ -16,7 +16,11 @@ services:
 # @see https://github.com/travis-ci/travis-ci/issues/8537#issuecomment-354020356
 sudo: required
 addons:
-  postgresql: 9.6
+  postgresql: "10"
+  apt:
+    packages:
+    - postgresql-10
+    - postgresql-client-10
 
 cache:
   yarn: true
@@ -29,9 +33,6 @@ before_install:
   - curl --location https://yarnpkg.com/install.sh | bash -s -- --version "$( node -e "console.log(require('./package.json').engines.yarn)" )"
   - export PATH="$HOME/.yarn/bin:$PATH"
 
-  # Upgrade to PostgreSQL 10.
-  - ./.travis-postgres10.sh
-
 install:
   - yarn --frozen-lockfile