Merge branch 'frozen-string-enable-lib-gitlab-i18n' into 'master'

Enable frozen string for spec/lib/gitlab/i18n

See merge request gitlab-org/gitlab!20669

spec/lib/gitlab/i18n/metadata_entry_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::I18n::MetadataEntry do

spec/lib/gitlab/i18n/po_linter_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'simple_po_parser'
 

spec/lib/gitlab/i18n/translation_entry_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::I18n::TranslationEntry do