Difference in file size not reported in 2.0

Created by: OskarPersson

Is this a bug report?

Yes

Did you try recovering your dependencies?

Yes

Environment

System:
  OS: macOS 10.14
  CPU: x64 Intel(R) Core(TM) i7-4650U CPU @ 1.70GHz
Binaries:
  Node: 8.11.4 - ~/.nvm/versions/node/v8.11.4/bin/node
  Yarn: 1.10.1 - /usr/local/bin/yarn
  npm: 5.6.0 - ~/.nvm/versions/node/v8.11.4/bin/npm
Browsers:
  Chrome: 69.0.3497.100
  Firefox: 62.0
  Safari: 12.0
npmPackages:
  react: ^16.5.2 => 16.5.2
  react-dom: ^16.5.2 => 16.5.2
  react-scripts: 1.1.5 => 1.1.5
npmGlobalPackages:
  create-react-app: Not Found

Steps to Reproduce

(Write your steps here:)

1. create new app
2. build app
3. make minor change in JS or CSS
4. build app

Expected Behavior

Difference in file sizes after gzip is reported on yarn build:

> yarn build
yarn run v1.10.1
react-scripts build
Creating an optimized production build...
Compiled successfully.

File sizes after gzip:

  36.99 KB (+36.3 KB)  build/static/js/main.cd85f7f2.js
  416 B (-7 B)         build/static/css/main.a7c7d0be.css

Actual Behavior

Difference in file sizes after gzip is not reported on yarn build

> yarn build
yarn run v1.10.1
react-scripts build
Creating an optimized production build...
Compiled successfully.

File sizes after gzip:

  36.99 KB  build/static/js/main.cd85f7f2.js
  416 B         build/static/css/main.a7c7d0be.css