Fix RuboCop offense

Author: wvengen

lib/rails_admin/config/fields/types/active_storage.rb

@@ -18,9 +18,7 @@ class ActiveStorage < RailsAdmin::Config::Fields::Types::FileUpload
           end
 
           register_instance_option :image? do
-            if value
-              value.representable? || mime_type(value.filename).to_s.match?(/^image/)
-            end
+            value && (value.representable? || mime_type(value.filename).to_s.match?(/^image/))
           end
 
           register_instance_option :eager_load do

lib/rails_admin/config/fields/types/multiple_active_storage.rb

@@ -23,9 +23,7 @@ class ActiveStorageAttachment < RailsAdmin::Config::Fields::Types::MultipleFileU
             end
 
             register_instance_option :image? do
-              if value
-                value.representable? || mime_type(value.filename).to_s.match?(/^image/)
-              end
+              value && (value.representable? || mime_type(value.filename).to_s.match?(/^image/))
             end
 
             def resource_url(thumb = false)