node-sass and sass-loader - Module build failed: TypeError: this.getResolve is not a function at Object.loader

You have "webpack": "^3.12.0" and "sass-loader": "^8.0.0", which I believe is incompatible (as discussed in this Github issue).

To solve the problem, either upgrade webpack to version 4 or downgrade sass-loader to version 7 (which, personally, is what I did).