fix(): custom collection in config

[ledniy]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #954

What is the new behavior?

Following order of collection resolving: command --collection option -> config collection -> fallback

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[ledniy]

@kamilmysliwiec Hi, any chance for review? We really wanna use our custom collection through the nest cli :)

[jmcdo29]

LGTM

[kamilmysliwiec]

LGTM