build-optimizer caches node-modules

[Flexns]

Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

Area

- [x] devkit
- [ ] schematics

Versions

Win 10
node: v8.9.4
npm: 6.0.0
angular-devkit/build-optimizer@0.6.1

Repro steps

1. npm update [dependency-to-update]
2. ng build --aot --build-optimizer
3. ng build --aot

The log given by the failure

The build run WITH build-optimizer does NOT include the changes inside the generated vendor.js file.
The build run WITHOUT build-optimizer does include the desired changes.

Desired functionality

build-optimizer should not use cached vendor.js code for updated node-modules

Mention any other details that might be useful

The node-module dependency that i used for the test was build with ng build, then published via NPM to a local Nexus.
It didn't matter whether i changed the whole code or just added a comment, the build with build-optimizer always stayed the same.