Formatter: Fix formatting <% else %> in inline mode

[marcoroth]

This pull request fixes a bug in the formatter, where we accidentally visited the end_node twice, instead of the subsequent node.

This following document

<span>
  <% if valid? %>
    Valid
  <% else %>
    Invalid
  <% end %>
</span>

was previously formatter to:

<span><% if valid? %>Valid<% end %><% end %></span>

Now it gets correctly formatted as:

<span><% if valid? %>Valid<% else %>Invalid<% end %></span>

Resolves #789

[tk0miya]

Thank you for the quick fix!