got it working again

weirdly enough yarn stopped installing all the correct bin files.
I was missing the javascript file that hooked the app into the page, 
etc.

package.json

@@ -3,13 +3,13 @@
   "version": "1.0.0",
   "devDependencies": {
     "npm-run-all": "^4.1.5",
-    "rollup": "^1.10.1",
-    "rollup-plugin-commonjs": "^9.3.4",
+    "rollup": "^1.12.1",
+    "rollup-plugin-commonjs": "^10.0.0",
     "rollup-plugin-livereload": "^1.0.0",
-    "rollup-plugin-node-resolve": "^4.2.3",
+    "rollup-plugin-node-resolve": "^5.2.0",
     "rollup-plugin-svelte": "^5.0.3",
     "rollup-plugin-terser": "^4.0.4",
-    "sirv-cli": "^0.4.0",
+    "sirv-cli": "^0.4.4",
     "svelte": "^3.0.0"
   },
   "scripts": {

rollup.config.js

@@ -0,0 +1,50 @@
+import svelte from 'rollup-plugin-svelte';
+import resolve from 'rollup-plugin-node-resolve';
+import commonjs from 'rollup-plugin-commonjs';
+import livereload from 'rollup-plugin-livereload';
+import { terser } from 'rollup-plugin-terser';
+
+const production = !process.env.ROLLUP_WATCH;
+
+export default {
+	input: 'src/main.js',
+	output: {
+		sourcemap: true,
+		format: 'iife',
+		name: 'app',
+		file: 'public/bundle.js'
+	},
+	plugins: [
+		svelte({
+			// enable run-time checks when not in production
+			dev: !production,
+			// we'll extract any component CSS out into
+			// a separate file  better for performance
+			css: css => {
+				css.write('public/bundle.css');
+			}
+		}),
+
+		// If you have external dependencies installed from
+		// npm, you'll most likely need these plugins. In
+		// some cases you'll need additional configuration 
+		// consult the documentation for details:
+		// https://github.com/rollup/rollup-plugin-commonjs
+		resolve({
+			browser: true,
+			dedupe: importee => importee === 'svelte' || importee.startsWith('svelte/')
+		}),
+		commonjs(),
+
+		// Watch the `public` directory and refresh the
+		// browser on changes when not in production
+		!production && livereload('public'),
+
+		// If we're building for production (npm run build
+		// instead of npm run dev), minify
+		production && terser()
+	],
+	watch: {
+		clearScreen: false
+	}
+};

src/main.js

@@ -0,0 +1,7 @@
+import App from './Main.html';
+
+var app = new App({
+  target: document.body
+});
+
+export default app;