DEV: Increase max length of theme_field name column

Now that we have custom SCSS files with arbitrary names, it's easy to exceed 30 characters

app/models/theme_field.rb

@@ -471,7 +471,7 @@ end
 #  id               :integer          not null, primary key
 #  theme_id         :integer          not null
 #  target_id        :integer          not null
-#  name             :string(30)       not null
+#  name             :string(255)      not null
 #  value            :text             not null
 #  value_baked      :text
 #  created_at       :datetime         not null

db/migrate/20190423112954_increase_theme_field_name_length.rb

@@ -0,0 +1,5 @@
+class IncreaseThemeFieldNameLength < ActiveRecord::Migration[5.2]
+  def change
+    change_column :theme_fields, :name, :string, limit: 255
+  end
+end