power_stencil fails on a system where git is not installed at all

power_stencil fails on a system where git is not installed at all with the following error:

/tmp $ power_stencil -V
Traceback (most recent call last):
        11: from /usr/local/bin/power_stencil:23:in `<main>'
        10: from /usr/local/bin/power_stencil:23:in `load'
         9: from /var/lib/gems/2.5.0/gems/power_stencil-0.8.3/exe/power_stencil:4:in `<top (required)>'
         8: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
         7: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
         6: from /var/lib/gems/2.5.0/gems/power_stencil-0.8.3/lib/power_stencil.rb:4:in `<top (required)>'
         5: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
         4: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
         3: from /var/lib/gems/2.5.0/gems/git-1.5.0/lib/git.rb:25:in `<top (required)>'
         2: from /var/lib/gems/2.5.0/gems/git-1.5.0/lib/git/lib.rb:875:in `meets_required_version?'
         1: from /var/lib/gems/2.5.0/gems/git-1.5.0/lib/git/lib.rb:865:in `current_command_version'
/var/lib/gems/2.5.0/gems/git-1.5.0/lib/git/lib.rb:967:in `command': git  version   2>&1:sh: 1: git: not found (Git::GitExecuteError)

Error coming from the git gem.