False positive in nimble_operator rule

[marcelofabri]

New Issue Checklist

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

Describe the bug

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

$ swiftlint --path file.swift --enable-all-rules --no-cache | grep nimble
Loading configuration from '.swiftlint.yml'
Linting Swift files at paths file.swift
Linting 'file.swift' (1/1)
Done linting! Found 2 violations, 0 serious in 1 file.
file.swift:2:2: warning: Nimble Operator Violation: Prefer Nimble operator overloads over free matcher functions. (nimble_operator)

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.28.2
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Homebrew
• Paste your configuration file:

# insert yaml contents here

• Are you using nested configurations?
  If so, paste their relative paths and respective contents.

No

• Which Xcode version are you using (check xcode-select -p)?

10.1

• Do you have a sample that shows the issue? Run echo "[string here]" | swiftlint lint --no-cache --use-stdin --enable-all-rules
  to quickly test if your example is really demonstrating the issue. If your example is more
  complex, you can use swiftlint lint --path [file here] --no-cache --enable-all-rules.

// This triggers a violation:
foo.method {
    expect(value).to(equal(expectedValue), description: "Failed")
    return Bar(value: ())
}