doc: recommend Node 12

doc/development.md

 
 ## Building the sources
 
-Node.js >= 10 and npm >= 6 are required.
+Node.js >= 12 and npm >= 6 are required.
 
 On Debian/Ubuntu systems, the required packages can be installed with:
 ```

doc/manual-install.md

 make
 ```
 
-_NOTE: When installing on older distributions keep in mind that you need Node.js >= 10 and npm >= 6._
+_NOTE: When installing on older distributions keep in mind that you need Node.js >= 12 and npm >= 6._
 
 Edit host names in `/srv/jitsi-meet/config.js` (see also the example config file):
 ```