style: if ! changed by unless

- if ! changed by unless as it is more readable
- !object.blank? is equivalent to object.present?, also more readable

app/views/conference_registrations/_form.html.haml

@@ -7,7 +7,7 @@
           = @conference.title
   .row
     .col-md-8
-      - if !current_user
+      - unless current_user
         %legend
           %span
             =link_to('#signup', role: 'tab', "aria-controls" => "home", "data-toggle" => "tab") do

app/views/conference_registrations/_ticket.html.haml

@@ -5,7 +5,7 @@
         %h4.media-heading
           = ticket.title
         %h5.media-heading
-        -if !ticket.description.blank?
+        -unless ticket.description.blank?
           = markdown(ticket.description)
   %td.col-sm-1.col-md-1
     = text_field_tag("tickets[][#{ticket.id}]", 0, type: 'number', min: 0,