feat(): use process.env.PORT by default

[ahasall]

This will make sure that an application generated by the NestJS can be deployed to the cloud without any modification

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?

[ ] Bugfix
[x] 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?

The default port is 3000.
Issue Number: N/A

What is the new behavior?

The default port is process.env.PORT and will fallback to 3000

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[ahasall]

Oh didn't see PR #288

[kamilmysliwiec]

hey @ahasall! long time no speak :) hope you're doing well. Since we have a similar PR opened already (#288), I'll close this one