Add frozen_string_literal to recently-added files from the community

lib/banzai/filter/project_reference_filter.rb

+# frozen_string_literal: true
+
 module Banzai
   module Filter
     # HTML filter that replaces project references with links.

lib/banzai/reference_parser/project_parser.rb

+# frozen_string_literal: true
+
 module Banzai
   module ReferenceParser
     class ProjectParser < BaseParser

spec/lib/banzai/filter/project_reference_filter_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Banzai::Filter::ProjectReferenceFilter do

spec/lib/banzai/reference_parser/project_parser_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Banzai::ReferenceParser::ProjectParser do