Change travis.yml back to use `npm install`

The npm version that is running on travis.ci doesn't support `npm ci`
It looks the easy way to update the npm version is updating the
package-lock.json file.

.travis.yml

@@ -4,7 +4,7 @@ language:
 
 install:
   - bundle install
-  - npm ci
+  - npm install
 
 script:
   - npm run build