title: error: cannot convert value of type 'ObjCBool' to expected argument type 'Bool' on Swift 4.1.2 and Kitura on Ubuntu 16.04
body: <p>I have a plain vanilla Ubuntu 16.04 and installed OpenSSH, Curl and Swift 4.1.2 on it.
  The base example (swift package init --type executable) works but when I want to use Kitura framework I got a compile error if I 'swift build' it.</p>
  
  <p>The error:</p>
  
  <pre><code>/.build/checkouts/Kitura.git--4845395383860597130/Sources/Kitura/staticFileServer/FileServer.swift:138:21: error: cannot convert value of type 'ObjCBool' to expected argument type 'Bool'
              if !isDirectoryBool {
                  ^~~~~~~~~~~~~~~
  </code></pre>
  
  <p>error: terminated(1): /home/thewall/swift-4.1.2-RELEASE-ubuntu16.04/usr/bin/swift-build-tool -f /home/thewall/zSwift/.build/debug.yaml main output:</p>
  
  <p>My package.swift file looks like:</p>
  
  <blockquote>
    <p>import PackageDescription</p>
    
    <p>let package = Package(
       name: "zSwift",
       dependencies: [
      .package(url: "<a href="https://github.com/IBM-Swift/Kitura.git" rel="nofollow noreferrer">https://github.com/IBM-Swift/Kitura.git</a>", >.upToNextMinor(from: "2.1.0")),
       ],
       targets: [
           .target(
               name: "zSwift",
               dependencies: ["Kitura"]),
       ]
    )</p>
  </blockquote>
  
  <p>uname -a gives:</p>
  
  <p>Linux thewall 4.10.0-28-generic #32~16.04.2-Ubuntu SMP Thu Jul 20 10:19:48 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux</p>
  
  <p>Any ideas?</p>