[web] Switch sass-loader to modern API.

This prevents a warning message being issued by `npm run dev`.

Author: youngman-g

tx2-web/webpack.config.js

@@ -53,6 +53,7 @@ module.exports = {
                 {
                     loader: "sass-loader",
                     options: {
+                        api: "modern",
                         sourceMap: true,
                         warnRuleAsWarning: true,
                     }