fix(ios): properly pass port to env in xcodebuild

[szymonrybczak]

Summary:

Fixes #2228

When passing --port to run-ios command it is of type number:

cli/packages/cli-platform-apple/src/commands/runCommand/createRun.ts

Line 44 in 0e8cf75

port: number;

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Run this command:

node /path/to/react-native-cli/packages/cli/build/bin.js run-ios --port 8888

3. Simulator should connect to a dev server on 8888 port.

Online.Converter.video.Jan.7.mp4

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[szymonrybczak]

CI failure not related to changes, it is failing because it can't install Cocoapods, because of the issue with boost - (more context: facebook/react-native#42109)