docs(cubejs-client-ngx): update README to reflect Angular version change to 12+

Author: HaidarZ

packages/cubejs-client-ngx/README.md

@@ -7,7 +7,7 @@
 
 # Cube.js Angular Client
 
-Cube.js Angular is an Angular Module for Angular 6+.
+Cube.js Angular is an Angular Module for Angular 12+.
 
 [Learn more](https://github.com/cube-js/cube.js#getting-started)