Source map explorer showing incorrect bundle size

**I'm submitting a ...** (check one with "x")
```
[x ] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[ ] support request => Please do not submit support request here, instead see use [gitter](https://gitter.im/mgechev/angular2-seed) or [stackoverflow](https://stackoverflow.com/questions/tagged/angular2)
```

**Current behavior**

Running build task with source map explorer html file creation bundle size in application schema doesn't match real bundle file size.

**Expected behavior**

File sizes to match each other.

**Minimal reproduction of the problem with instructions**

Doing the following:
1. Clone angular-seed repository
2. npm run sme.prod.rollup.aot

Bundle size in dist folder:
http://imgur.com/a/4eDe2

Bundle size in source-map-explorer output file:
http://imgur.com/a/apcby

Shouldn't sizes match here?

* **Angular Seed Version:** `aaaaf75`

6f8a821

* **Node:** `node --version` =
v6.11.1

Run npm run sme.prod.rollup.aot in the angular-seed repository and compare the bundle size in dist with the size reported in the generated source-map explorer HTML output. Trace the build task and source-map explorer integration to identify why the values differ; done means the reported and actual file sizes match.

Written by the indexing model from the issue text.