ruby on rails tutorial 4版 3章

(ruby on rails tutorial 4版 3章のurl)
https://railstutorial.jp/chapters/static_pages?version=5.1#cha-static_pages

3.6　「高度なセットアップ」のなかでテストの自動化がうまくいきません。
・test/test_helper.rbにminitest-reporters gemを設定。
・bundle exec guard initで初期化。
・Guardfile.をカスタマイズ。
・.gitignoreにSpringを追加。
チュートリアルの手順に沿って、上記の作業を行い。bundle exec guardを実行しましたが
以下のエラーになりうまくいきません。以下のエラーの意味を教えてください。

/home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/guardfile/evaluator.rb:89:in evaluate': invalid byte sequence in UTF-8 (ArgumentError) from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard.rb:134:in _evaluate'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard.rb:49:in setup' from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/commander.rb:32:in start'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/cli/environments/valid.rb:16:in start_guard' from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/cli.rb:122:in start'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/thor-0.20.0/lib/thor/command.rb:27:in run' from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/thor-0.20.0/lib/thor/invocation.rb:126:in invoke_command'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/thor-0.20.0/lib/thor.rb:387:in dispatch' from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/thor-0.20.0/lib/thor/base.rb:466:in start'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/aruba_adapter.rb:32:in execute' from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/lib/guard/aruba_adapter.rb:19:in execute!'
from /home/vagrant/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/guard-2.13.0/bin/_guard-core:11:in `<main>'