chore(deps): update node:8.16.0 docker digest to ef9eec2

Author: renovate-bot

.circleci/config.yml

@@ -6,7 +6,7 @@ machine:
 jobs:
   build:
     docker:
-      - image: node:8.16.0@sha256:65c4ca91ca5e1a6b2947f3336e5190fdf93bfd70dd4aafdb07ae1111cdaa1044
+      - image: node:8.16.0@sha256:ef9eec21d7228c9df4bd6efb4ee7f4bd081db843b41718939843eb6e10a53f79
     environment:
       - NPM_CONFIG_LOGLEVEL: warn
     working_directory: ~/repo