Add update alias

Add `update` alias for `brew upgrade mas`. See mas-cli#281.

MasKit/Commands/Update.swift

@@ -0,0 +1,46 @@
+//
+//  Update.swift
+//  mas-cli
+//
+//  Created by Andrew Naylor on 30/12/2015.
+//  Copyright © 2015 Andrew Naylor. All rights reserved.
+//
+
+import Commandant
+import Foundation
+
+/// Command which updates mas.
+public struct UpdateCommand: CommandProtocol {
+    public typealias Options = NoOptions<MASError>
+    public let verb = "update"
+    public let function = "Update MAS"
+
+    private let appLibrary: AppLibrary
+
+    /// Public initializer.
+    /// - Parameter appLibrary: AppLibrary manager.
+    public init() {
+        self.init(appLibrary: MasAppLibrary())
+    }
+
+    /// Internal initializer.
+    /// - Parameter appLibrary: AppLibrary manager.
+    init(appLibrary: AppLibrary = MasAppLibrary()) {
+        self.appLibrary = appLibrary
+    }
+
+    /// Runs the command.
+    public func run(_: Options) -> Result<(), MASError> {
+        print("Updating MAS…")
+
+        let task = Process()
+        task.launchPath = getenv("HOMEBREW_BREW_FILE")
+        task.arguments = ["upgrade", "mas"]
+        //let pipe = Pipe()
+        //task.standardOutput = pipe
+        //task.standardError = pipe
+        task.launch()
+        task.waitUntilExit()
+        return task.terminationStatus
+    }
+}

mas/main.swift

@@ -37,6 +37,7 @@ registry.register(SignOutCommand())
 registry.register(UninstallCommand())
 registry.register(RemoveCommand())
 registry.register(RmCommand())
+registry.register(UpdateCommand())
 registry.register(UpgradeCommand())
 registry.register(VendorCommand())
 registry.register(VersionCommand())