Run the server in before_script

.travis.yml

@@ -3,6 +3,5 @@ node_js: 8
 cache:
   directories:
     - node_modules
-after_success:
-  - node -r esm index.js
-  - npx apollo schema:check --endpoint=http://localhost:$PORT
+before_script: node -r esm index.js &
+after_success: npx apollo schema:check --endpoint=http://localhost:$PORT