Add sourcemaps, fix Sass compilation.

package.json

@@ -12,6 +12,7 @@
     "build": "rollup -c && rollup -c rollup.config.min.js",
     "build-docs": "jsdoc2md -f src/dat/gui/GUI.js src/dat/controllers/Controller.js src/dat/controllers/NumberController.js | replace-between --target API.md --token API",
     "lint": "eslint src",
+    "preversion": "npm run lint",
     "version": "npm run build && git add -A build",
     "postversion": "git push && git push --tags && npm publish"
   },

rollup.config.js

@@ -26,10 +26,12 @@ export default {
     file: './build/dat.gui.js',
     format: 'umd',
     name: 'dat',
+    sourcemap: true,
     banner: banner
   }, {
     file: './build/dat.gui.module.js',
     format: 'es',
+    sourcemap: true,
     banner: banner
   }],
   watch: {
@@ -38,6 +40,7 @@ export default {
   plugins: [
     resolve(),
     sass({
+      insert: true,
       output: 'build/dat.gui.css',
       options: {outputStyle: 'compressed'}
     }),