chore(deps): update circleci/node:8 docker digest to 73537ec

Author: renovate-bot

.circleci/config.yml

@@ -6,7 +6,7 @@ machine:
 jobs:
   build:
     docker:
-      - image: circleci/node:8@sha256:82ffad866eaa9d2f55460446554d806480407180b7dde7b88063bfba71eb6bcc
+      - image: circleci/node:8@sha256:73537ec700458d76acba2efc3dd4027ba2094470b783ea39dd79dd6af56eea1a
       - image: mongo:3.7.9@sha256:736eec20a17eafaa988d299902fcaab521cb0ca56af4400f782576afc878d6bc
     environment:
       - NPM_CONFIG_LOGLEVEL: warn