ci(config): update the node image in CirceCI (#517)

To takle the [failing build](https://github.com/all-contributors/all-contributors/runs/2336473172)
following the _successful_ merge of #514

Author: Berkmann18

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2.1
 
 docker_defaults: &docker_defaults
   docker:
-    - image: circleci/node:8.14.0
+    - image: circleci/node:12.0.0
 
 commands:
   prep_env: