add alias for booth

Booth can be replaced with any alias by replacing it in alias.en.yml. This change is introduced as some events do not use booth but uses other words such as stand.

spec/controllers/admin/booths_controller_spec.rb

@@ -75,7 +75,7 @@ describe Admin::BoothsController do
         end
 
         it 'shows success message' do
-          expect(flash[:notice]).to match('Booth successfully created.')
+          expect(flash[:notice]).to match("#{(t 'booth').capitalize} successfully created.")
         end
 
         it 'creates a new user on inviting booth responsible' do
@@ -106,7 +106,7 @@ describe Admin::BoothsController do
         end
 
         it 'shows flash message' do
-          expect(flash[:error]).to eq("Creating booth failed. Title can't be blank.")
+          expect(flash[:error]).to eq("Creating #{t 'booth'} failed. Title can't be blank.")
         end
       end
     end
@@ -131,7 +131,7 @@ describe Admin::BoothsController do
         end
 
         it 'shows success message' do
-          expect(flash[:notice]).to match 'Successfully updated booth.'
+          expect(flash[:notice]).to match "Successfully updated #{t 'booth'}."
         end
 
         it 'updates booth' do