Change label from iOS to ObjC (#3398)
Change label from iOS to ObjC (#3398)

Summary:
The documentation shows Swift and ObjC code, but the label names are Swift and iOS.

## Changelog
Modify the documentation

Pull Request resolved: https://github.com/facebook/flipper/pull/3398

Test Plan:
No test plan

**Static Docs Preview: flipper**
|[Full Site](https://our.intern.facebook.com/intern/staticdocs/eph/D34269458/V2/flipper/)|

|**Modified Pages**|
|[docs/getting-started/ios-native](https://our.intern.facebook.com/intern/staticdocs/eph/D34269458/V2/flipper/docs/getting-started/ios-native/)|

Reviewed By: mweststrate

Differential Revision: D34269458

Pulled By: aigoncharov

fbshipit-source-id: 98909b539b49a54eb6cba8605b55a00e53619a19

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