With the option, assert_enqueued_jobs will check the number of times a specific kind of job is enqueued.

Indent the list content by 4 spaces instead of 2 to match the other
changelog files. Also wrap the lines around 80 chars.

Finally update the documentation example with nit-picky things.

We will support only Ruby >= 2.1.

But right now we don't accept pull requests with syntax changes to drop
support to Ruby 1.9.