Exclude trailing_comma validation on single-line declarations

[ZevEisenberg]

The typical arguments for requiring a trailing comma in arrays and dictionaries is so that adding or removing elements doesn't dirty adjacent lines in source control. However, that argument doesn't hold for single-line declarations such as this one I just came across in a project:

static let componentsToZeroForDay: [Calendar.Component] = [.hour, .minute, .second, .nanosecond]

It would be nice for SwiftLint to ignore cases like this. There could potentially be a separate rule that all arrays and dictionaries must be multiline, but I personally would leave that one off.

[ZevEisenberg]

The existing warning is also annoying in cases of single-element arrays, like this:

let components = calendar.dateComponents([Calendar.Component.day], from: from, to: to)

By the way, my SwiftLint configuration includes:

trailing_comma:
  mandatory_comma: true

[jpsim]

Should be pretty easy to only report errors in single-line multi-line arrays and dictionaries.

[ZevEisenberg]

Single-line? Don't you mean multi-line?

[jpsim]

Yes, sorry, updated.

[jpsim]

Fixed by @marcelofabri in #912.