Update Node.js version used for development and CI to 16

The previous 10.x version is EOL. 16.x is the newest version in LTS status. LTS seems the most appropriate choice for
the needs of this project.

Author: per1234

.github/CONTRIBUTING.md

@@ -9,6 +9,8 @@
 Follow the installation instructions here:<br />
 https://nodejs.dev/download
 
+Node.js 16.x is used for development of this project. [nvm](https://github.com/nvm-sh/nvm) is recommended to easily switch between Node.js versions.
+
 ### 2. Install dependencies
 
 To work on the codebase you have to install all the dependencies:

.github/workflows/check-npm.yml

@@ -2,7 +2,7 @@ name: Check npm
 
 env:
   # See: https://github.com/actions/setup-node/#readme
-  NODE_VERSION: 10.x
+  NODE_VERSION: 16.x
 
 # See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
 on:

.github/workflows/check-packaging-ncc-typescript-npm.yml

@@ -2,7 +2,7 @@ name: Check Packaging
 
 env:
   # See: https://github.com/actions/setup-node/#readme
-  NODE_VERSION: 10.x
+  NODE_VERSION: 16.x
 
 on:
   push:

.github/workflows/test.yml

@@ -1,5 +1,9 @@
 name: Test Action
 
+env:
+  # See: https://github.com/actions/setup-node/#readme
+  NODE_VERSION: 16.x
+
 on:
   push:
   pull_request:
@@ -24,10 +28,10 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: Set Node.js 10.x
+      - name: Setup Node.js
         uses: actions/setup-node@v2
         with:
-          node-version: 10.x
+          node-version: ${{ env.NODE_VERSION }}
 
       - name: npm install
         run: npm install