Use some modern ruby-isms for rake/gemspec

Rakefile

-require "bundler/gem_tasks"
-require "rake/testtask"
+#!/usr/bin/env rake
+# frozen_string_literal: true
+
+require 'bundler/gem_tasks'
+require 'rake/testtask'
 
 Rake::TestTask.new(:test) do |t|
-  t.libs << "test"
-  t.libs << "lib"
+  t.libs << 'test'
+  t.libs << 'lib'
   t.test_files = FileList['test/**/*_test.rb']
 end
 
-task :default => :test
+task default: :test

foreman_uuid_boot.gemspec

 # frozen_string_literal: true
 
-lib = File.expand_path('lib', __dir__)
-$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
-require 'foreman_uuid_boot/version'
+require_relative 'lib/foreman_uuid_boot/version'
 
 Gem::Specification.new do |spec|
   spec.name          = 'foreman_uuid_boot'