Update Nimble dependency to 8.0.0..<9.0.0

[phlippieb]

Linenoise depends on Nimble, and specifies 7.0.1 upwards as the required version. This creates a conflict in packages that also depend on nimble, but are using the more recent 8.* versions.

For example, the following simple Package.swift...

// swift-tools-version:5.1
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "swiftpm",
    dependencies: [
        .package(url: "https://github.com/andybest/linenoise-swift.git", from: "0.0.0"),
        .package(url: "https://github.com/Quick/Nimble.git", from: "8.0.0")
    ],
    targets: [which this package depends on.
        .target(
            name: "swiftpm",
            dependencies: ["LineNoise", "Nimble"]),
        .testTarget(
            name: "swiftpmTests",
            dependencies: ["swiftpm"]),
    ]
)

... fails with the error:

error: the package dependency graph could not be resolved; possibly because of these requirements:    https://github.com/andybest/linenoise-swift.git @ 0.0.0..<1.0.0

[phlippieb]

#14