SwiftLint: False positive: let_var_whitespace with Swift 5.1 property wrappers

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

I have adopted the new Swift 5.1 property wrapper feature. It seems to cause a false positive with the opt-in rule let_var_whitespace.

Relevant file:

import Foundation

public enum Defaults {

    @UserDefault("isFirstTimeUser", defaultValue: true)
    public static var isFirstTimeUser: Bool
}

Complete output when running SwiftLint, including the stack trace and command used

$ swiftlint lint --config ../.swiftlint.yml 
Loading configuration from '../.swiftlint.yml'
Linting Swift files at paths 
Linting 'Defaults.swift' (1/1)
<path>/Defaults.swift:6:5: warning: Variable Declaration Whitespace Violation: Let and var should be separated from other statements by a blank line. (let_var_whitespace)
Done linting! Found 1 violation, 0 serious in 1 files.

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.37.0
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Homebrew
• Paste your configuration file:

opt_in_rules:
  - let_var_whitespace

• Are you using nested configurations? No
• Which Xcode version are you using? 11.2.1
• Do you have a sample that shows the issue?

echo "public enum Defaults {
@UserDefault("isFirstTimeUser", defaultValue: true)
public static var isFirstTimeUser: Bool
}" | swiftlint lint --no-cache --use-stdin --enable-all-rules