ng doc <keyword> not working

[KissBalazs]

Versions

Angular CLI: 6.0.0
Node: 9.4.0
OS: linux x64
Angular: 6.0.0
... animations, cli, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, platform-server, router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.6.0
@angular-devkit/build-angular     0.6.0
@angular-devkit/build-optimizer   0.6.0
@angular-devkit/core              0.6.0
@angular-devkit/schematics        0.6.0
@ngtools/webpack                  6.0.0
@schematics/angular               0.6.0
@schematics/update                0.6.0
rxjs                              6.1.0
typescript                        2.7.2
webpack                           4.6.0

Repro steps

• type the command ng doc hello

Observed behavior

opn_1.default is not a function
TypeError: opn_1.default is not a function
    at DocCommand.<anonymous> (/home/forest/Projects/ui-concept/node_modules/@angular/cli/commands/doc.js:41:33)
    at Generator.next (<anonymous>)
    at /home/forest/Projects/ui-concept/node_modules/@angular/cli/commands/doc.js:7:71
    at new Promise (<anonymous>)
    at __awaiter (/home/forest/Projects/ui-concept/node_modules/@angular/cli/commands/doc.js:3:12)
    at DocCommand.run (/home/forest/Projects/ui-concept/node_modules/@angular/cli/commands/doc.js:36:16)
    at /home/forest/Projects/ui-concept/node_modules/@angular/cli/models/command-runner.js:278:30
    at Generator.next (<anonymous>)
    at fulfilled (/home/forest/Projects/ui-concept/node_modules/@angular/cli/models/command-runner.js:4:58)
    at <anonymous>

Desired behavior

Should be able to see some kind of documentation? Or default at least?

Mention any other details that might be useful (optional)

Just updated to angular 6, never tried that command before.

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