Progress bar helper broken on future reservations

[orenyk]

2018-01-12T16:02:37.993061+00:00 app[web.1]:   Rendered reservations/show.html.erb within layouts/application (450.1ms)
2018-01-12T16:02:37.994035+00:00 app[web.1]: Completed 500 Internal Server Error in 596ms (ActiveRecord: 92.1ms)
2018-01-12T16:02:38.000284+00:00 app[web.1]:   
2018-01-12T16:02:38.000288+00:00 app[web.1]: ActionView::Template::Error (can't modify frozen String):
2018-01-12T16:02:38.000506+00:00 app[web.1]:     100:                   <div class="col-md-12">
2018-01-12T16:02:38.000509+00:00 app[web.1]:     101:                     <div class="progress">
2018-01-12T16:02:38.000510+00:00 app[web.1]:     102:                       <%= content_tag :div, class: 'progress-bar', style: "width: " << bar_progress_res do %>
2018-01-12T16:02:38.000511+00:00 app[web.1]:     103:                         <%= content_tag :span, reservation_length_in_words, style: bar_span_positioning_fix %>
2018-01-12T16:02:38.000513+00:00 app[web.1]:     104:                       <% end %>
2018-01-12T16:02:38.000514+00:00 app[web.1]:     105:                       <%# TODO: extract to a helper method? %>
2018-01-12T16:02:38.000515+00:00 app[web.1]:     106:                       <% unless reservation_length > 31 %>
2018-01-12T16:02:38.000516+00:00 app[web.1]:   
2018-01-12T16:02:38.000518+00:00 app[web.1]: app/helpers/reservations_helper.rb:39:in `bar_span_positioning_fix'
2018-01-12T16:02:38.000519+00:00 app[web.1]: app/views/reservations/show.html.erb:103:in `block in _app_views_reservations_show_html_erb__3351597263680270778_54811620'
2018-01-12T16:02:38.000520+00:00 app[web.1]: app/views/reservations/show.html.erb:102:in `_app_views_reservations_show_html_erb__3351597263680270778_54811620'