Remove empty lines from membership.md

[ghost]

Empty lines seem to be upsetting the {% raw %} content, and some DOM elements are being rendered as text.

I'm not 100% sure that this'll fix it, but the markdown preview no longer has any weird <pre>-formatted sections, so that's a start...

Below is a snippet (with source) from the rendered page:

      <!-- end membership form -->

      &lt;/div&gt;
      <aside class="sidebar" role="complementary">
        <!-- reserved for future use -->
      </aside>
    &lt;/div&gt;
  &lt;/div&gt;

&lt;/div&gt;

[hblankenship]

The empty spaces did not seem to impact the dangling divs. Found and fixed a missing end tag in member_benefits.md that resolved this issue. Thank you for your contribution.