Rake task to update verse difficulty is broken. So is Sidekiq job.

[avitus]

=== Updating verse difficulty at 2016-12-14 14:55:19 -0800 ===
Difficulty Ranges for Each Translation

NIV : 99.79 - 1.49
TMB : 72.73 - 2
rake aborted!
ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'NaN' in 'field list': UPDATE verses SET difficulty = NaN, updated_at = '2016-12-14 23:11:20' WHERE verses.id = 6943