Allow opening brace on newline in case of multiline class or struct

[revolter]

[SwiftLintBot]

	1 Warning
:warning:	Please include a CHANGELOG entry to credit yourself! You can find it at CHANGELOG.md.

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Here's an example of your CHANGELOG entry:

* Allow opening brace on newline in case of multiline class or struct.  
  [revolter](https://github.com/revolter)
  [#issue_number](https://github.com/realm/SwiftLint/issues/issue_number)

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