Use @handlebars/parser v2

We have to remove `--failAfterWarnings` from our Rollup integration-test,
because Typescript, when targeting es5, will use global `this` for transpilation.
Rollup warns about this, since it replaces `this` with `undefined`:

```
src/index.js → dist/bundle.js...
(!) `this` has been rewritten to `undefined`
https://rollupjs.org/guide/en/#error-this-is-undefined
../../../node_modules/@handlebars/parser/dist/esm/printer.js
1: var __spreadArrays = (this && this.__spreadArrays) || function () {}
```

See https://github.com/handlebars-lang/handlebars-parser/releases/tag/v2.0.0

package.json

@@ -20,7 +20,7 @@
     "node": ">=12"
   },
   "dependencies": {
-    "@handlebars/parser": "^1.1.0",
+    "@handlebars/parser": "^2.1.0",
     "neo-async": "^2.6.2",
     "source-map": "^0.6.1",
     "yargs": "^16.2.0"

tests/integration/rollup-test/package.json

@@ -3,7 +3,7 @@
   "description": "Various tests with Handlebars and rollup",
   "version": "1.0.0",
   "scripts": {
-    "build": "rollup --config rollup.config.js --failAfterWarnings"
+    "build": "rollup --config rollup.config.js"
   },
   "private": true,
   "devDependencies": {