fixes bug in setting slug on container

app/models/container.rb

@@ -1,6 +1,6 @@
 class Container < ActiveRecord::Base
   extend FriendlyId
-  friendly_id :container_slug, use: %i(slugged finders)
+  friendly_id :description, use: %i(slugged finders)
 
   has_many :plots, dependent: :destroy
   has_many :gardens, through: :plots
@@ -8,7 +8,7 @@ class Container < ActiveRecord::Base
   validates :description, presence: true, uniqueness: true
 
   def container_slug
-    "#{self.description}".gsub!(/[^A-Za-z ]/, '')
+    description.gsub!(/[^A-Za-z ]/, '')
   end
 
   def subtitler(container)

db/schema.rb

@@ -171,6 +171,8 @@ ActiveRecord::Schema.define(version: 20181201213214) do
     t.string   "slug"
   end
 
+  add_index "containers", ["slug"], name: "index_containers_on_slug", unique: true, using: :btree
+
   create_table "crops", force: :cascade do |t|
     t.string   "name",                                              null: false
     t.string   "en_wikipedia_url"