feat(docker): Use node 10 in the Docker image.

fixes #6973

.travis.yml

@@ -1,8 +1,6 @@
 language: node_js
 
-node_js:
-  - "8"
-  - "10"
+node_js: "10"
 
 services:
   - redis-server

Dockerfile-build

@@ -1,4 +1,4 @@
-FROM node:8-alpine
+FROM node:10-alpine
 
 RUN npm install -g npm@6 && rm -rf ~app/.npm /tmp/*