Update circleci/node:9 Docker digest to a7b28f (#153)

renovate[bot] · calebeby · commit 7d30f7e0bedb · 2018-05-29T18:03:31.000-07:00
diff --git a/.circleci/config.yml b/.circleci/config.yml
@@ -2,7 +2,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: circleci/node:9@sha256:e81a1e0709e12f506c73abde7c8a9ba16a0ac50477f7e3237ea388cbc620a56a
+      - image: circleci/node:9@sha256:a7b28f4d11171e5e9faef06d562b2bdf908ec4f13eb6af7570870d642740d27e
 
     working_directory: ~/repo
 
