Simplify gemspec load path setup using require_relative.

Author: ppostma

docdata-order.gemspec

@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
-lib = File.expand_path('lib', __dir__)
-$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
-require 'docdata/order/version'
+require_relative 'lib/docdata/order/version'
 
 Gem::Specification.new do |spec|
   spec.name          = 'docdata-order'