Bump node from 12.15.0-alpine to 12.16.0-alpine in /alpine

Bumps node from 12.15.0-alpine to 12.16.0-alpine.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

alpine/Dockerfile

-FROM node:12.15.0-alpine
+FROM node:12.16.0-alpine
 
 # Build arguments to change source url, branch or tag
 ARG CODIMD_REPOSITORY=https://github.com/codimd/server.git