Avoid warnings on Swift 5.1

[giginet]

Short description 📝

This project raises some warnings on Xcode 11 toolchain.

$ swift build
 XcodeProj (master) ~ swift build
'XcodeProj' /Users/giginet/.ghq/github.com/tuist/XcodeProj: warning: the target name XcodeProj has different case on the filesystem and the Package.swift manifest file
'XcodeProj' /Users/giginet/.ghq/github.com/tuist/XcodeProj: warning: the target name XcodeProjTests has different case on the filesystem and the Package.swift manifest file
/Users/giginet/.ghq/github.com/tuist/XcodeProj/Sources/XcodeProj/Utils/PBXBatchUpdater.swift:122:13: warning: variable 'components' was never mutated; consider changing to 'let' constant
        var components = groupPath.components
        ~~~ ^
        let
/Users/giginet/.ghq/github.com/tuist/XcodeProj/Sources/XcodeProj/Utils/ReferenceGenerator.swift:327:37: warning: 'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range upto' operator.
            return String(reference.substring(to: reference.index(reference.startIndex, offsetBy: 24)))
                                    ^
/Users/giginet/.ghq/github.com/tuist/XcodeProj/Sources/XcodeProj/Extensions/String+md5.swift:28:32: warning: 'withUnsafeBytes' is deprecated: use `withUnsafeBytes<R>(_: (UnsafeRawBufferPointer) throws -> R) rethrows -> R` instead
            let message = data.withUnsafeBytes { bytes -> [UInt8] in
                               ^
/Users/giginet/.ghq/github.com/tuist/XcodeProj/Sources/XcodeProj/Extensions/String+md5.swift:218:17: warning: variable 'M' was never mutated; consider changing to 'let' constant
            var M = toUInt32Array(chunk)
            ~~~ ^
            let
[4/4] Merging module XcodeProj

Solution 📦

This PR make changes to avoid some warnings.

Implementation 👩‍💻👨‍💻

• Use let instead of var.
• String.substring(to:) is deprecated. Use Swift.Range instead
• Data.withUnsafeBytes is deprecated. Use instead another overload.