chore: switch to dart-sass (#2441)

package.json

@@ -18,7 +18,7 @@
     "build:js:rollup": "rollup -c",
     "build:js:uglify": "uglifyjs htdocs/js/c3.js --compress --mangle --comments -o htdocs/js/c3.min.js",
     "build:css": "run-s build:css:sass build:css:min",
-    "build:css:sass": "node-sass src/scss/main.scss > htdocs/css/c3.css",
+    "build:css:sass": "sass src/scss/main.scss > htdocs/css/c3.css",
     "build:css:min": "cleancss -o htdocs/css/c3.min.css htdocs/css/c3.css",
     "build:docs": "bundle exec middleman build",
     "publish-docs": "npm run build:docs && gh-pages -d build -m \"chore: update gh-pages [skip ci]\"",
@@ -72,12 +72,12 @@
     "karma-coverage-istanbul-reporter": "^2.0.0",
     "karma-jasmine": "^1.1.0",
     "karma-spec-reporter": "0.0.32",
-    "node-sass": "^4.8.3",
     "node-static": "^0.7.9",
     "nodemon": "^1.11.0",
     "npm-run-all": "^4.1.3",
     "rollup": "^0.63.0",
     "rollup-plugin-babel": "^3.0.3",
+    "sass": "^1.10.3",
     "status-back": "^1.1.0",
     "uglify-js": "^3.3.17",
     "watchify": "^3.11.0"