Add a dummy entry point for rollup

When specifying a package for code splitting, rollup requires the
packages to have a valid entry point for some reason.

Add an empty one.

packages/common/index.js

+// dummy entry point

packages/common/package.json

 {
   "name": "vpu-common",
   "version": "1.0.1",
+  "module": "index.js",
   "devDependencies": {
     "karma": "^4.2.0",
     "karma-chai": "^0.1.0",
@@ -18,7 +19,7 @@
   },
   "scripts": {
     "clean": "rm dist/*",
-    "build": "npm run build-local",
+    "build": "rollup -c",
     "build-test": "rollup -c --environment BUILD:test",
     "test": "npm run build-test && karma start --singleRun"
   },

packages/common/rollup.config.js

@@ -7,7 +7,7 @@ const build = (typeof process.env.BUILD !== 'undefined') ? process.env.BUILD : '
 console.log("build: " + build);
 
 export default {
-    input: 'test/**/*.js',
+    input: (build !='test') ? 'index.js' : 'test/**/*.js',
     output: {
         file: 'dist/bundle.js',
         format: 'esm'