Install based on starter kit broken

### Issue type

**I'm submitting a ...** (check one with "x")

* [X] bug report
* [ ] feature request

### Issue description

**Current behavior:**

https://akveo.github.io/nebular/docs/guides/install-based-on-starter-kit#install-based-on-starter-kit
Follow the instructions exactly and install fails. npm saas is deprecated? I am new to Angular and wanted something that was partially done. Surprised that I couldn't even install the sample code following the instructions exactly using Ubuntu 20 LTS.
**Expected behavior:**

The sample application works. It installs without error
**Steps to reproduce:**

Go to https://akveo.github.io/nebular/docs/guides/install-based-on-starter-kit#install-based-on-starter-kit
Follow the setup instructions exactly.
When you get to npm i, it will fail.

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! node-sass@4.12.0 postinstall: `node scripts/build.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the node-sass@4.12.0 postinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /root/.npm/_logs/2021-01-11T18_41_10_226Z-debug.log
**Related code:**

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### Other information:

**npm, node, OS, Browser**
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**Angular, Nebular**
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