Fix CircleCI configuration

CircleCI sent me an email indicating that the config settings for this
repo were set to use a deprecated image (Ubuntu 14.04) because we didn't
specify the image to use.

The image option is required, per their docs; set it as recommended.

Author: BrianHawley

.circleci/config.yml

@@ -3,6 +3,7 @@ version: 2
 jobs:
   test:
     machine:
+      image: ubuntu-2204
       docker_layer_caching: true
     working_directory: ~/codeclimate/codeclimate-rubocop
     steps:
@@ -12,6 +13,7 @@ jobs:
 
   release_images:
     machine:
+      image: ubuntu-2204
       docker_layer_caching: true
     working_directory: ~/codeclimate/codeclimate-rubocop
     steps: