chore: remove old Node versions from the readme (#549)

Signed-off-by: Lucas Holmquist <[email protected]>

Author: lholmquist

README.md

@@ -19,7 +19,7 @@ _Note:_ Supports CloudEvent version 1.0
 ## Installation
 
 The CloudEvents SDK requires a current LTS version of Node.js. At the moment
-those are Node.js 12.x, Node.js 14.x, Node.js 16.x, and Node.js 18.x. To install in your Node.js project:
+those are Node.js 16.x, and Node.js 18.x. To install in your Node.js project:
 
 ```console
 npm install cloudevents