calculateTree() runs forever if PR has 1000+ files

In index.tsx calculateTree() you parseInt the contents of `files_tab_counter`, but GitHub formats it with a comma (e.g. 1024 -> "1,024"), so parseInt returns the value before the first comma.

As a result, count is always greater than fileCount and we retrigger calculateTree over and over again:
```
if (fileCount !== count) {
setTimeout(this.calculateTree.bind(this), 100)
}
```