`<%= %>` and `<% %>` have the same functionality

[kcajf]

https://github.com/mpastell/Pweave/blob/45b56ec60c5badb4e40796178397a4eae5bdddcb/pweave/processors/base.py#L251

It looks like the self.add_echo() from this line went missing at some point. Now, <%= %> and <% %> have the same functionality (code is the same).