chore: Update Node.js version (#2849)

Dockerfile

@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1.2
 ARG APP_PATH=/opt/outline
-FROM node:14-alpine AS deps-common
+FROM node:16-alpine AS deps-common
 
 ARG APP_PATH
 WORKDIR $APP_PATH
@@ -17,7 +17,7 @@ RUN yarn install --production=true --frozen-lockfile && \
   yarn cache clean
 
 # ---
-FROM node:14-alpine AS builder
+FROM node:16-alpine AS builder
 
 ARG APP_PATH
 WORKDIR $APP_PATH
@@ -28,7 +28,7 @@ ARG CDN_URL
 RUN yarn build
 
 # ---
-FROM node:14-alpine AS runner
+FROM node:16-alpine AS runner
 
 ARG APP_PATH
 WORKDIR $APP_PATH

README.md

@@ -87,7 +87,7 @@ For contributing features and fixes you can quickly get an environment running u
 
 1. Install these dependencies if you don't already have them
    1. [Docker for Desktop](https://www.docker.com)
-   1. [Node.js](https://nodejs.org/) (v12 LTS preferred)
+   1. [Node.js](https://nodejs.org/) (v16 LTS preferred)
    1. [Yarn](https://yarnpkg.com)
 1. Clone this repo
 1. Register a Slack app at https://api.slack.com/apps