Use iife format for Rollup (#141)

Author: ankane

lib/install/rollup/rollup.config.js

@@ -4,7 +4,7 @@ export default {
   input: "app/javascript/application.js",
   output: {
     file: "app/assets/builds/application.js",
-    format: "es",
+    format: "iife",
     inlineDynamicImports: true,
     sourcemap: true
   },