global undefined in process polyfill

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used [patch-package](https://github.com/ds300/patch-package) to patch `rollup-plugin-node-polyfills@0.2.1` for the project I'm working on.

'process' polyfill fails for me at runtime trying to reference 'global'. There is a separate polyfill for 'global', so I just referenced that in the process polyfill and it resolved my issue.

Here is the diff that solved my problem:

```diff
diff --git a/node_modules/rollup-plugin-node-polyfills/polyfills/process-es6.js b/node_modules/rollup-plugin-node-polyfills/polyfills/process-es6.js
index b7205a5..47de4a7 100644
--- a/node_modules/rollup-plugin-node-polyfills/polyfills/process-es6.js
+++ b/node_modules/rollup-plugin-node-polyfills/polyfills/process-es6.js
@@ -1,6 +1,9 @@
// shim for using process in browser
// based off https://github.com/defunctzombie/node-process/blob/master/browser.js

+import global from "./global";
+
+
function defaultSetTimout() {
throw new Error('setTimeout has not been defined');
}
```

This issue body was [partially generated by patch-package](https://github.com/ds300/patch-package/issues/296).

Read polyfills/process-es6.js and polyfills/global.js, then trace how the process polyfill resolves global in a browser runtime. Done means the process polyfill no longer fails with an undefined global while preserving its existing behavior.

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