RuntimeError: can't modify frozen String

[irees]

https://sentry.io/mapzen/datastore-prod/issues/184231952/

Net::OpenTimeout: execution expired
  app/services/feed_fetcher_service.rb:106:in `fetch_and_normalize_feed_version'
    gtfs = GTFS::Source.build(
  app/services/feed_fetcher_service.rb:54:in `fetch_and_return_feed_version'
    feed_version = fetch_and_normalize_feed_version(feed)
  app/workers/feed_fetcher_worker.rb:11:in `perform'
    feed_version = FeedFetcherService.fetch_and_return_feed_version(feed)
...
(41 additional frame(s) were not displayed)

GTFS::InvalidSourceException: execution expired
  app/services/feed_fetcher_service.rb:106:in `fetch_and_normalize_feed_version'
    gtfs = GTFS::Source.build(
  app/services/feed_fetcher_service.rb:54:in `fetch_and_return_feed_version'
    feed_version = fetch_and_normalize_feed_version(feed)
  app/workers/feed_fetcher_worker.rb:11:in `perform'
    feed_version = FeedFetcherService.fetch_and_return_feed_version(feed)
...
(31 additional frame(s) were not displayed)

RuntimeError: can't modify frozen String
  app/services/feed_fetcher_service.rb:45:in `block in fetch_and_return_feed_version'
    fetch_exception_log << "\n"
  app/services/feed_fetcher_service.rb:62:in `rescue in fetch_and_return_feed_version'
    error_handler.call(e, 'feed_fetch_invalid_source')
  app/services/feed_fetcher_service.rb:67:in `fetch_and_return_feed_version'
    end
  app/workers/feed_fetcher_worker.rb:11:in `perform'
    feed_version = FeedFetcherService.fetch_and_return_feed_version(feed)
...
(27 additional frame(s) were not displayed)

RuntimeError: can't modify frozen String