method_missing: undefined method `increment_open_transactions` database_cleaner

When using database_cleaner (0.9.1) with rails (4.1.0)

{my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/dynamic_matchers.rb:26:in `method_missing': undefined method `increment_open_transactions' for ActiveRecord::Base:Class (NoMethodError)
    from {my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/database_cleaner-0.9.1/lib/database_cleaner/active_record/transaction.rb:13:in `start'
    from {my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/database_cleaner-0.9.1/lib/database_cleaner/base.rb:73:in `start'
    from {my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/database_cleaner-0.9.1/lib/database_cleaner/configuration.rb:75:in `block in start'
    from {my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/database_cleaner-0.9.1/lib/database_cleaner/configuration.rb:75:in `each'
    from {my home path}/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/database_cleaner-0.9.1/lib/database_cleaner/configuration.rb:75:in `start'

Somehow we were using an old version of database_cleaner,

gem "database_cleaner",   "~> 0.9.1"

because the fix was authored a year ago.

gem "database_cleaner", "~> 1.2.0"

I guess that will teach me to dig too deeply before simply trying the latest version of a gem.