Undetected duplicates across bundles

According to the [multiple entry points](https://github.com/FormidableLabs/inspectpack/tree/917c7c9ba5118ae19b5992ed0afd505dbf6ba460#note-multiple-entry-points) section in the readme, inspectpack will analyse all of the bundled files across all of the entry points. However, as of v4.5.2, this doesn't work as expected for me.

I've set up a reduced test case in https://github.com/tlvince/tlvince-sandbox-webpack-duplicates - there are two entry points each pulling in a different version of lodash. Inspectpack does not seem to detect these:

```
❯ yarn inspectpack -s dist/stats.json -a versions
yarn run v1.22.10
$ /tmp/tlvince-sandbox-webpack-duplicates/node_modules/.bin/inspectpack -s dist/stats.json -a versions
inspectpack --action=versions
=============================

## Summary
* Packages with skews: 0
* Total resolved versions: 0
* Total installed packages: 0
* Total depended packages: 0
* Total bundled files: 0
Done in 0.20s.
```

Another tool, webpack-stats-duplicates, does:

```
❯ yarn webpack-stats-duplicates dist/stats.json
yarn run v1.22.10
$ /tmp/tlvince-sandbox-webpack-duplicates/node_modules/.bin/webpack-stats-duplicates dist/stats.json
Duplicate module lodash found in webpack configuration 0
./packages/a/node_modules/lodash
./packages/b/node_modules/lodash
```

In the bundle analyser report:


Am I missing something or is this unsupported?