Update recommended Node version for development

As of April 19th, 2024, the CI is using Node 20.12.0 for testing.
Node <18 no longer works with some dependencies that were recently
updated, namely chromedriver 116.0.1 -> 119.0.1.

Author: dlarocque

README.md

@@ -29,8 +29,7 @@ Please see [Environment Support](https://firebase.google.com/support/guides/envi
 #### Node.js
 
 Before you can start working on the Firebase JS SDK, you need to have Node.js
-installed on your machine. As of June 13th, 2023 the team has been testing with Node.js versions
-between `16.4.0` and `16.16.0`, but the required verison of Node.js may change as we update
+installed on your machine. As of April 19th, 2024 the team has been testing with Node.js version 20.12.2, but the required verison of Node.js may change as we update
 our dependencies.
 
 To download Node.js visit https://nodejs.org/en/download/.
@@ -64,7 +63,7 @@ $ yarn -v
 $ java -version
 ```
 
-Your `node` version should be between `16.4.0` and `16.6.0`, your `yarn` version should
+Your `node` version should be `20.12.2`, your `yarn` version should
 be between `1.0.0` and `1.22.11`, and your `java` version should be `11.0` or greater.
 
 _NOTE: We will update the documentation as new versions are required, however