chore: consistent CI build files

.travis.yml

@@ -16,6 +16,9 @@ notifications:
 node_js:
 - node
 
+install:
+  - npm ci
+
 script: 
 - npm run build
 - npm test

appveyor.yml

@@ -12,7 +12,7 @@ cache:
   - '%AppData%\..\Local\Cypress\Cache -> package-lock.json'
 
 install:
-  - npm install
+  - npm ci
 
 before_build:
   # Output useful info for debugging.