False positive on SortedFirstLastRule (sorted_first_last) with firstIndex(of:), firstIndex(where:), lastIndex(of:) and lastIndex(where:) method.

[r-plus]

New Issue Checklist

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

Describe the bug

func index(of element: Element) -> AnyIndex? method is deprecated in Xcode 10.2.
Its method should migrate to func firstIndex(of element: Element) -> AnyIndex?.
Since I migrated my code, SwiftLint warnings about SortedFirstLastRule.

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

$ echo "keys.sorted().firstIndex(of: idx)" | swiftlint lint --no-cache --use-stdin --enable-all-rules
Loading configuration from '.swiftlint.yml'
<nopath>:1:1: warning: Min or Max over Sorted First or Last Violation: Prefer using `min()` or `max()` over `sorted().first` or `sorted().last` (sorted_first_last)
Done linting! Found 1 violation, 0 serious in 1 file.

And also lastIndex(of:)

$ echo "keys.sorted().lastIndex(of: idx)" | swiftlint lint --no-cache --use-stdin --enable-all-rules
Loading configuration from '.swiftlint.yml'
<nopath>:1:1: warning: Min or Max over Sorted First or Last Violation: Prefer using `min()` or `max()` over `sorted().first` or `sorted().last` (sorted_first_last)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.31.0
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Homebrew
• Paste your configuration file:

opt_in_rules:
  - sorted_first_last

• 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)? 10.2
• 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:
keys.sorted().firstIndex(of: idx)
keys.sorted().lastIndex(of: idx)