angular-seed SCSS error

**I'm submitting a ...** (check one with "x")
```
[ x] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[ ] support request => Please do not submit support request here, instead see use [gitter](https://gitter.im/mgechev/angular2-seed) or [stackoverflow](https://stackoverflow.com/questions/tagged/angular2)
```

**Current behavior**

I'm following the guide (Working with SASS)[https://github.com/mgechev/angular-seed/wiki/Working-with-SASS] and the following error throws.

`[12:53:07] Starting 'build.html_css'...
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type object
at assertPath (path.js:39:11)
at Object.dirname (path.js:1268:5)
at Object.importer (/home/alobaton/workspace/GOSTOCK/gostock-web/angular-seed/node_modules/node-sass-magic-importer/src/index.ts:92:32)
at options.importer (/home/alobaton/workspace/GOSTOCK/gostock-web/angular-seed/node_modules/node-sass/lib/index.js:336:31)`

**Expected behavior**

Compile with out problems.

**Please tell us about your environment:**

SO: Ubuntu 18.04.1 LTS 64 Bits
RAM: 11,1 GiB
Processor: AMD® A10-9600p radeon r5, 10 compute cores 4c+6g × 4

* **Angular Seed Version:** `aaaaf75`
latest
* **Node:** `node --version` =
v10.13.0

Start with the Working with SASS guide and reproduce the build.html_css failure using Node v10.13.0 on Ubuntu 18.04. Inspect the node-sass-magic-importer and node-sass stack frames shown in the report. Done means the SASS build completes without the invalid path argument error.

Written by the indexing model from the issue text.