def template
      File.read("#{Dir.home}/.gem_updater_template.erb")
    rescue Errno::ENOENT
      File.read(File.expand_path('../lib/gem_updater_template.erb', __dir__))
    end
def template
      File.read("#{Dir.home}/.gem_updater_template.erb")
    rescue Errno::ENOENT
      File.read(File.expand_path('../lib/gem_updater_template.erb', __dir__))
    end
Get the template for gem's diff.
 It can use a custom template.

 @return [ERB] the template