Specify required ruby version to 2.2.6 or greater

[unasuke]

Itamae is dependent by specinfra that's version is 2.64.0 or greater currently.
Specinfra requires net-ssh gem version 2.7 or greater and net-ssh gem requires ruby version 2.2.6 or greater.
Therefore itamae requires ruby 2.2.6 or greater as practically.
This pull request does specify the required ruby version to gemspec for end-user helpful.

supplement

My investigation article (ja_JP) ➡️ https://note.mu/unasuke/n/n5fe89607c517

[sue445]

net-ssh gem requires ruby version 2.2.6 or greater.

net-ssh 5.2.0 is yes, but net-ssh 2.7.0 is no.

• https://rubygems.org/gems/net-ssh/versions/5.2.0
• https://rubygems.org/gems/net-ssh/versions/2.7.0

net-ssh 2.7.0 is available in ruby 2.1

Example

# Gemfile
source "https://rubygems.org"

gem "itamae", "1.10.4"
gem "specinfra", "2.64.0"
gem "net-ssh", "2.7.0"

$ ruby -v
ruby 2.1.10p492 (2016-04-01 revision 54464) [x86_64-darwin16.0]

$ bundle install --path vendor/bundle
Fetching gem metadata from https://rubygems.org/.........
Resolving dependencies...
Fetching ansi 1.5.0
Installing ansi 1.5.0
Using bundler 1.17.1
Fetching hashie 3.6.0
Installing hashie 3.6.0
Fetching schash 0.1.2
Installing schash 0.1.2
Fetching net-ssh 2.7.0
Installing net-ssh 2.7.0
Fetching net-scp 2.0.0
Installing net-scp 2.0.0
Fetching net-telnet 0.1.1
Installing net-telnet 0.1.1
Fetching sfl 2.3
Installing sfl 2.3
Fetching specinfra 2.64.0
Installing specinfra 2.64.0
Fetching thor 0.20.3
Installing thor 0.20.3
Fetching itamae 1.10.4
Installing itamae 1.10.4
Bundle complete! 3 Gemfile dependencies, 11 gems now installed.
Bundled gems are installed into `./vendor/bundle`

If ruby 2.1 user want to install itamae, install net-ssh 2.7.0 before install itamae

$ gem install net-ssh -v 2.7.0
Fetching: net-ssh-2.7.0.gem (100%)
Successfully installed net-ssh-2.7.0
Building YARD (yri) index for net-ssh-2.7.0...
Done installing documentation for net-ssh after 1 seconds
1 gem installed

$ gem install itamae
Fetching: sfl-2.3.gem (100%)
Successfully installed sfl-2.3
Fetching: net-telnet-0.1.1.gem (100%)
Successfully installed net-telnet-0.1.1
Fetching: net-scp-2.0.0.gem (100%)
Successfully installed net-scp-2.0.0
Fetching: specinfra-2.77.2.gem (100%)
Successfully installed specinfra-2.77.2
Fetching: hashie-3.6.0.gem (100%)
Successfully installed hashie-3.6.0
Fetching: ansi-1.5.0.gem (100%)
Successfully installed ansi-1.5.0
Fetching: schash-0.1.2.gem (100%)
Successfully installed schash-0.1.2
Fetching: itamae-1.10.4.gem (100%)
Successfully installed itamae-1.10.4
Building YARD (yri) index for ansi-1.5.0...
[warn]: Could not find file: QED.rdoc
Building YARD (yri) index for hashie-3.6.0...
Building YARD (yri) index for itamae-1.10.4...
Building YARD (yri) index for net-scp-2.0.0...
Building YARD (yri) index for net-telnet-0.1.1...
Building YARD (yri) index for schash-0.1.2...
Building YARD (yri) index for sfl-2.3...
Building YARD (yri) index for specinfra-2.77.2...
Done installing documentation for ansi, hashie, itamae, net-scp, net-telnet, schash, sfl, specinfra after 3 seconds
8 gems installed