fix: access process from globalThis (#14)

Fixes webpack error:

```
Module not found: Error: Can't resolve 'process/browser' in /path/...
```

Falls back to `setImmediate`, then `setTimeout`.

src/index.js

@@ -244,7 +244,7 @@ export class BlockstoreDatastoreAdapter extends BaseBlockstore {
 
     // process.nextTick runs on the microtask queue, setImmediate runs on the next
     // event loop iteration so is slower. Use process.nextTick if it is available.
-    const runner = process && process.nextTick ? process.nextTick : setImmediate
+    const runner = globalThis.process && globalThis.process.nextTick ? globalThis.process.nextTick : (globalThis.setImmediate || globalThis.setTimeout)
 
     runner(async () => {
       try {