add relationships for booths

app/models/conference.rb

@@ -22,6 +22,7 @@ class Conference < ActiveRecord::Base
   has_many :supporters, through: :ticket_purchases, source: :user
   has_many :tickets, dependent: :destroy
   has_many :resources, dependent: :destroy
+  has_many :booths,  dependent: :destroy  
 
   has_many :lodgings, dependent: :destroy
   has_many :registrations, dependent: :destroy