Serverspecのインストールができない

[Rindrics]

初版の書籍で勉強しております。すばらしい本を出版してくださり、ありがとうございます。
初版p.82の「AnsibleによるServerspecのインストール」でつまづいたので、報告させて下さい。

[vagrant@demo ansible-playbook-sample]$ ansible-playbook -i development site.yml
[DEPRECATION WARNING]: The TRANSFORM_INVALID_GROUP_CHARS settings is set to
allow bad characters in group names by default, this will change, but still be
user configurable on deprecation. This feature will be removed in version 2.10.
 Deprecation warnings can be disabled by setting deprecation_warnings=False in
ansible.cfg.
[WARNING]: Invalid characters were found in group names but not replaced, use
-vvvv to see details


PLAY [webservers] **************************************************************

TASK [Gathering Facts] *********************************************************
ok: [localhost]

TASK [common : install epel] ***************************************************
ok: [localhost]

TASK [nginx : install nginx] ***************************************************
ok: [localhost]

TASK [nginx : replace index.html] **********************************************
ok: [localhost]

TASK [nginx : nginx start] *****************************************************
ok: [localhost]

TASK [serverspec : install ruby] ***********************************************
ok: [localhost]

TASK [serverspec : install serverspec] *****************************************
failed: [localhost] (item=rake) => {"ansible_loop_var": "item", "changed": false, "cmd": "/bin/gem install --no-user-install --no-document rake", "item": "rake", "msg": "ERROR:  Error installing rake:\n\trake requires Ruby version >= 2.2.", "rc": 1, "stderr": "ERROR:  Error installing rake:\n\trake requires Ruby version >= 2.2.\n", "stderr_lines": ["ERROR:  Error installing rake:", "\trake requires Ruby version >= 2.2."], "stdout": "", "stdout_lines": []}
failed: [localhost] (item=serverspec) => {"ansible_loop_var": "item", "changed": false, "cmd": "/bin/gem install --no-user-install --no-document serverspec", "item": "serverspec", "msg": "ERROR:  Error installing serverspec:\n\tnet-ssh requires Ruby version >= 2.2.6.", "rc": 1, "stderr": "ERROR:  Error installing serverspec:\n\tnet-ssh requires Ruby version >= 2.2.6.\n", "stderr_lines": ["ERROR:  Error installing serverspec:", "\tnet-ssh requires Ruby version >= 2.2.6."], "stdout": "", "stdout_lines": []}

PLAY RECAP *********************************************************************
localhost                  : ok=6    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0

[vagrant@demo ansible-playbook-sample]$