Simplify the method and fix Rubocop warnings

app/controllers/admin/tags_controller.rb

@@ -9,13 +9,8 @@ class Admin::TagsController < Admin::BaseController
   end
 
   def create
-    @existing_tag = Tag.where(name: tag_params.first).first
-    if @existing_tag
-      @existing_tag.kind = "category"
-      @existing_tag.save
-    else
-      Tag.category.create(tag_params)
-    end
+    Tag.find_or_create_by!(name: tag_params["name"]).update!(kind: "category")
+
     redirect_to admin_tags_path
   end
 

spec/features/admin/tags_spec.rb

@@ -90,7 +90,7 @@ describe "Admin tags" do
   end
 
   scenario "Upgrade tag to category" do
-    not_category_tag = create(:tag, name: "Soon a category")
+    create(:tag, name: "Soon a category")
 
     visit admin_tags_path
 
@@ -101,5 +101,4 @@ describe "Admin tags" do
 
     expect(page).to have_content "Soon a category"
   end
-
 end