Fix rubocop Style/ExpandPathArguments

Addressing:
openscap.gemspec:2:14: C: Style/ExpandPathArguments: Use expand_path('lib/openscap/version', __dir__) instead of expand_path('../lib/openscap/version', __FILE__).
require File.expand_path('../lib/openscap/version', __FILE__)
             ^^^^^^^^^^^

Author: isimluk

openscap.gemspec

@@ -1,5 +1,5 @@
 require 'date'
-require File.expand_path('../lib/openscap/version', __FILE__)
+require File.expand_path('lib/openscap/version', __dir__)
 
 GEMSPEC = Gem::Specification.new do |gem|
   gem.name = 'openscap'