Remove ruby 2.4 warnings

[mogox]

bundle exec rake
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
[DEPRECATION] `last_comment` is deprecated.  Please use `last_description` instead.
/home/travis/.rvm/rubies/ruby-2.4.1/bin/ruby -w -S rspec spec/ail_segment_spec.rb spec/aip_segment_spec.rb spec/basic_parsing_spec.rb spec/batch_parsing_spec.rb spec/child_segment_spec.rb spec/core_ext/date_time_spec.rb spec/default_segment_spec.rb spec/dg1_spec.rb spec/dynamic_segment_def_spec.rb spec/err_segment_spec.rb spec/evn_segment_spec.rb spec/fts_segment_spec.rb spec/in1_segment_spec.rb spec/message_spec.rb spec/messages_spec.rb spec/mfe_segment_spec.rb spec/mfi_segment_spec.rb spec/msa_segment_spec.rb spec/msh_segment_spec.rb spec/nk1_segment_spec.rb spec/obr_segment_spec.rb spec/obx_segment_spec.rb spec/orc_segment_spec.rb spec/pid_segment_spec.rb spec/prd_segment_spec.rb spec/pv1_segment_spec.rb spec/rf1_segment_spec.rb spec/sch_segment_spec.rb spec/segment_field_spec.rb spec/segment_generator_spec.rb spec/segment_list_storage_spec.rb spec/segment_spec.rb spec/sft_segment_spec.rb spec/spec_helper.rb spec/speed_parsing_spec.rb spec/spm_segment_spec.rb
/home/travis/.rvm/rubies/ruby-2.4.1/lib/ruby/site_ruby/2.4.0/bundler/definition.rb:557: warning: instance variable @new_platform not initialized
/home/travis/.rvm/rubies/ruby-2.4.1/lib/ruby/site_ruby/2.4.0/bundler/definition.rb:533: warning: instance variable @new_platform not initialized
/home/travis/.rvm/rubies/ruby-2.4.1/lib/ruby/site_ruby/2.4.0/bundler/definition.rb:533: warning: instance variable @new_platform not initialized
/home/travis/build/ruby-hl7/ruby-hl7/vendor/bundle/ruby/2.4.0/gems/rspec-core-2.99.2/lib/rspec/core/configuration.rb:172: warning: method redefined; discarding old pattern=
/home/travis/build/ruby-hl7/ruby-hl7/vendor/bundle/ruby/2.4.0/gems/rspec-core-2.99.2/lib/rspec/core/configuration.rb:255: warning: method redefined; discarding old treat_symbols_as_metadata_keys_with_true_values=
/home/travis/build/ruby-hl7/ruby-hl7/vendor/bundle/ruby/2.4.0/gems/rspec-core-2.99.2/lib/rspec/core/ruby_project.rb:27: warning: File.exists? is a deprecated name, use File.exist? instead
/home/travis/build/ruby-hl7/ruby-hl7/vendor/bundle/ruby/2.4.0/gems/simplecov-html-0.7.1/lib/simplecov-html.rb:57: warning: assigned but unused variable - title_id

https://travis-ci.org/ruby-hl7/ruby-hl7/jobs/367968975