chore(package): add package-lock.json (#454)

Author: felixfbecker

.gitignore

@@ -6,4 +6,3 @@ coverage/
 *.iml
 npm-debug.log
 yarn.lock
-package-lock.json

.npmrc

@@ -8,6 +8,12 @@ cache:
   directories:
     - $HOME/.npm
 
+before_install:
+  - npm install -g npm@6.0.0
+
+install:
+  - npm ci
+
 script:
   - npm run lint
   - npm run build