Update Node.js from 18.20.3 to 20.19.2

Node 18 is reaching its end of life on April 30th, 2025, so we're
updating in order to keep using a maintained version after that date.

docs/en/README.md

@@ -12,7 +12,7 @@ You can access the main website of the project at [http://consuldemocracy.org](h
 
 **NOTE**: For more detailed instructions, check the [local installation docs](installation/local_installation.md).
 
-Prerequisites: install git, Ruby 3.3.8, CMake, pkg-config, Node.js 18.20.3, ImageMagick and PostgreSQL (>=9.5).
+Prerequisites: install git, Ruby 3.3.8, CMake, pkg-config, Node.js 20.19.2, ImageMagick and PostgreSQL (>=9.5).
 
 **Note**: The `bin/setup` command below might fail if you've configured a username and password for PostgreSQL. If that's the case, edit the lines containing `username:` and `password:` (adding your credentials) in the `config/database.yml` file and run `bin/setup` again.
 

docs/en/installation/deploying-on-heroku.md

@@ -64,7 +64,7 @@ This tutorial assumes that you have already managed to clone Consul Democracy on
 
   ```json
   "engines": {
-    "node": "18.20.3"
+    "node": "20.19.2"
   }
   ```