In version 3.0 of middleman, you've been able to use the variables development? and build? in templates. In version 4.0 these variables no longer exist.
How do I identify which environment middleman is currently running in?
Middleman v4.0 uses a new method of identifying which environment it is currently running in. This is because you can now have more than two environments.
Old syntax:
<% if development? %>
...
<% end %>
New syntax:
<% if config[:environment].eql?(:development) %>
...
<% end %>