Update ci (#139)

This PR updates the CircleCI configuration. The following changes were made:

Update to latest node orb
Update matrix of node versions to latest of each tested version
Add 15.x to node matrix
Change base docker image since npm wouldn't install with the node executor 🤷
Note: Node 12.x tests should be removed on approximately 11/30 when it moves to maintenance.

.circleci/config.yml

@@ -1,9 +1,10 @@
 version: 2.1
 orbs:
-  node: circleci/node@3.0.1
+  node: circleci/node@4.1.0
 jobs:
   test:
-    executor: node/default
+    docker:
+      - image: cimg/base:stable
     parameters:
       node-version:
         type: string
@@ -34,6 +35,7 @@ workflows:
           matrix:
             parameters:
               node-version:
-                - 12.18.0
+                - 12.19.0
                 - 13.14.0
-                - 14.5.0
+                - 14.15.0
+                - 15.1.0