update minimum node version

.github/workflows/js.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [9.x, 13.x]
+        node-version: [10.x, 13.x]
 
     steps:
     - uses: actions/checkout@v2

README.md

@@ -88,7 +88,7 @@ The core of reveal.js is very easy to install. You'll simply need to download a
 
 Some reveal.js features, like external Markdown and speaker notes, require that presentations run from a local web server. The following instructions will set up such a server as well as all of the development tasks needed to make edits to the reveal.js source code.
 
-1. Install [Node.js](https://nodejs.org/) (9.0.0 or later)
+1. Install [Node.js](https://nodejs.org/) (10.0.0 or later)
 
 1. Clone the reveal.js repository
    ```sh

package.json

@@ -21,7 +21,7 @@
     "url": "git://github.com/hakimel/reveal.js.git"
   },
   "engines": {
-    "node": ">=9.0.0"
+    "node": ">=10.0.0"
   },
   "devDependencies": {
     "@babel/core": "^7.8.7",