chore: update rollup

Update rollup and plugins, and remove some plugins. We'll use Rollup for
now only to bundle and minify our code, but otherwise we'll write
reasonably modern code and not need a transform.

Author: trusktr

build/build.js

@@ -1,9 +1,8 @@
-import rollup from 'rollup';
-import buble from 'rollup-plugin-buble';
-import commonjs from 'rollup-plugin-commonjs';
-import nodeResolve from 'rollup-plugin-node-resolve';
-import { uglify } from 'rollup-plugin-uglify';
-import replace from 'rollup-plugin-replace';
+import * as rollup from 'rollup';
+import commonjs from '@rollup/plugin-commonjs';
+import nodeResolve from '@rollup/plugin-node-resolve';
+import uglify from '@rollup/plugin-terser';
+import replace from '@rollup/plugin-replace';
 import chokidar from 'chokidar';
 import path from 'path';
 import { relative } from './util.js';
@@ -28,10 +27,6 @@ async function build(opts) {
     .rollup({
       input: opts.input,
       plugins: (opts.plugins || []).concat([
-        buble({
-          transforms: {
-            dangerousForOf: true
-          }}),
         commonjs(),
         nodeResolve(),
         replace({