Bug Report or Feature Request (mark with an x)

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

Area

- [ ] devkit
- [x] schematics

Versions

Angular CLI: 6.0.8
Node: 8.11.2
OS: win32 x64
Angular: 6.0.7
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.6.8
@angular-devkit/build-angular     0.6.8
@angular-devkit/build-optimizer   0.6.8
@angular-devkit/core              0.6.8
@angular-devkit/schematics        0.6.8
@angular/cli                      6.0.8
@ngtools/webpack                  6.0.8
@schematics/angular               0.6.8
@schematics/update                0.6.8
rxjs                              6.2.1
typescript                        2.7.2
webpack                           4.8.3

Repro steps

1. Add projects/architect/<section>/options/invalid options to options in angular.json eg

   "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "invalid": "value", 
            ...
          }
   }
   

2. Run ng build

Actual functionality

Schema validation failed with the following errors:
  Data path "" should NOT have additional properties(invalid).

Desired functionality

Schema validation failed with the following errors:
  Data path "path/to/invalid/option" should NOT have additional properties(invalid).