swift package update で特定のライブラリがFetchされる現象について

Question

おはようございます。
もしご存知の方がいたらよろしくお願いします。

◎困っている事
1.swift package update 実行で Package.swift にない ShellOut というライブラリが Fetch される。
(Clone はされない)
2.MacOS では問題無いが、Ubuntu では Fetch の途中で止まってしまう。

◎解決したい事
最終的には何らかの SMTP, Neo4j 用のライブラリを Ubuntu 上の Swift に組み込みたいのですが、
今回の質問では、そもそも Package.swift にないライブラリがなぜ Fetch されてしまうのかを知りたいです。

◎環境
・Swift 4.1
・Xcode 9.4.1
・MacOS 10.13.5
・Ubuntu 16.04.4

◎現象が起きるコマンド

※最後にある swift package update を Ubuntu で実行すると、途中で止まります。
もし確認して頂ける方がいたら注意して下さい。

$ cd ~
$ mkdir Sample
$ cd Sample/
$ swift package init --type executable

（Package.swift を以下のように編集する）

// swift-tools-version:4.0
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "Sample",
    dependencies: [
        .package(url: "https://github.com/IBM-Swift/Swift-SMTP.git", from: "4.0.0"),
        .package(url: "https://github.com/Neo4j-Swift/Neo4j-Swift.git", from: "4.0.0"),
    ],
    targets: [
        .target(
            name: "Sample",
            dependencies: []),
    ]
)

$ swift package update

---

◎ swift package update の実行結果

・ MacOS
Fetching https://github.com/IBM-Swift/Swift-SMTP.git
Fetching https://github.com/Neo4j-Swift/Neo4j-Swift.git
Fetching https://github.com/IBM-Swift/BlueSocket.git
Fetching https://github.com/IBM-Swift/BlueSSLService.git
Fetching https://github.com/IBM-Swift/BlueCryptor.git
Fetching https://github.com/IBM-Swift/LoggerAPI.git
Fetching https://github.com/IBM-Swift/CommonCrypto.git
Fetching https://github.com/Neo4j-Swift/Bolt-swift.git
Fetching https://github.com/antitypical/Result.git
Fetching https://github.com/Neo4j-Swift/PackStream-swift.git
Fetching https://github.com/JohnSundell/ShellOut.git
Cloning https://github.com/Neo4j-Swift/Neo4j-Swift.git
Resolving https://github.com/Neo4j-Swift/Neo4j-Swift.git at 4.0.2
Cloning https://github.com/IBM-Swift/CommonCrypto.git
Resolving https://github.com/IBM-Swift/CommonCrypto.git at 1.0.0
Cloning https://github.com/IBM-Swift/BlueSSLService.git
Resolving https://github.com/IBM-Swift/BlueSSLService.git at 0.12.84
Cloning https://github.com/Neo4j-Swift/Bolt-swift.git
Resolving https://github.com/Neo4j-Swift/Bolt-swift.git at 1.0.3
Cloning https://github.com/IBM-Swift/LoggerAPI.git
Resolving https://github.com/IBM-Swift/LoggerAPI.git at 1.7.3
Cloning https://github.com/IBM-Swift/BlueSocket.git
Resolving https://github.com/IBM-Swift/BlueSocket.git at 0.12.94
Cloning https://github.com/Neo4j-Swift/PackStream-swift.git
Resolving https://github.com/Neo4j-Swift/PackStream-swift.git at 1.0.2
Cloning https://github.com/IBM-Swift/BlueCryptor.git
Resolving https://github.com/IBM-Swift/BlueCryptor.git at 1.0.4
Cloning https://github.com/antitypical/Result.git
Resolving https://github.com/antitypical/Result.git at 3.2.4
Cloning https://github.com/IBM-Swift/Swift-SMTP.git
Resolving https://github.com/IBM-Swift/Swift-SMTP.git at 4.0.0

（ Fetch のみされて、このあと問題無くコンパイルまで出来る ）

・ Ubuntu
Fetching https://github.com/IBM-Swift/Swift-SMTP.git
Fetching https://github.com/Neo4j-Swift/Neo4j-Swift.git
Fetching https://github.com/IBM-Swift/BlueSocket.git
Fetching https://github.com/IBM-Swift/BlueSSLService.git
Fetching https://github.com/IBM-Swift/BlueCryptor.git
Fetching https://github.com/IBM-Swift/LoggerAPI.git
Fetching https://github.com/IBM-Swift/OpenSSL.git
Fetching https://github.com/Neo4j-Swift/Bolt-swift.git
Fetching https://github.com/antitypical/Result.git
Fetching https://github.com/Neo4j-Swift/PackStream-swift.git
Fetching https://github.com/JohnSundell/ShellOut.git

（ Fetch されて、ここで止まってしまう。３分ほど待ったが動き無し）

---

よろしくお願いします。