Require files in TestResultFile (#30)

Author: xprazak2

lib/openscap_parser/test_result_file.rb

@@ -1,4 +1,7 @@
 # frozen_string_literal: true
+require 'openscap_parser/xml_file'
+require 'openscap_parser/benchmarks'
+require 'openscap_parser/test_results'
 
 module OpenscapParser
   # A class to represent an XmlFile which contains a <TestResult /> Xccdf type