Fixes commenting on interpolated elixir tags

[fklement]

As using <%# some content %> as block comment doesn't really work well in .html.eex templates i changed them to the normal html block comment tags.

Comments before (wrong):
<%# <%= form_for @conn, initiate_path(@conn, :create), [errors: @conn.assigns[:errors]], fn f -> %> %>
Comments now (right):
<!-- <%= form_for @conn, initiate_path(@conn, :create), [errors: @conn.assigns[:errors]], fn f -> %> -->

Commenting in .html.eex templates now works as it should for me.