Add `acronym` example to default `inflections.rb`

If you search for “api” at Github (✓&l=Ruby) you will notice a mix use of lowercase and uppercase of API word. Given it is widely used acronym, I wonder if we could add it as an example into default generated inflections.rb.

So it might look like:

# ActiveSupport::Inflector.inflections(:en) do |inflect|
# ...

inflect.acronym ‘API’

# end