Prefer npm ci

I noticed that `npm install` is used instead of `npm ci` when building my static web app. It's an Angular app that I setup, and I would prefer it if the build would use `npm ci` to install the packages from the package-lock.json file so that I am sure versions don't shift around.

Here's the log I'm seeing:

```
Using Node version:
v14.15.1

Using Npm version:
6.14.8

Installing production dependencies in '/working_dir/mystaticwebapp/.oryx_prod_node_modules'...

Running 'npm install --unsafe-perm --production'...
added 86 packages from 83 contributors and audited 1632 packages in 12.251s

4 packages are looking for funding
run `npm fund` for details

found 0 vulnerabilities

Copying production dependencies from '/working_dir/mystaticwebapp/.oryx_prod_node_modules' to '/working_dir/mystaticwebapp/node_modules'...
Done in 0 sec(s).

Running 'npm install --unsafe-perm'...
```