Add path arugment to rake task for updating versions list file

usage:
rake compact_index:update_versions_file["path_to_file/versions.list"]

lib/tasks/compact_index.rake

@@ -91,9 +91,9 @@ namespace :compact_index do
   end
 
   desc "Generate/update the versions.list file"
-  task update_versions_file: :environment do
-    file_path = Rails.application.config.rubygems['versions_file_location']
-    versions_file = CompactIndex::VersionsFile.new file_path
+  task :update_versions_file, [:file_path] => :environment do |_t, args|
+    raise "#{args[:file_path]} does not exist" unless File.exist?(args[:file_path])
+    versions_file = CompactIndex::VersionsFile.new args[:file_path]
 
     # Only indexed versions of a gem go into *new* versions file
     query = ["SELECT r.name, v.created_at as date, v.info_checksum, v.number, v.platform