Merge branch 'ci-config' into 'master'

Configure Continuous Integration

Closes #8

See merge request !5

.gitlab-ci.yml

+image: registry.gitlab.com/tomjorquera/runner_node-chromium:latest
+
+stages:
+  - test
+
+test:
+  script:
+    - yarn run ci

package.json

@@ -7,7 +7,8 @@
   "scripts": {
     "start": "node app.js",
     "test": "xo && jest",
-    "test:watch": "jest --watch"
+    "test:watch": "jest --watch",
+    "ci": "yarn && xo && jest --runInBand"
   },
   "dependencies": {
     "mz": "2.6.0",