cordova plugin list prints helper message to STDOUT instead of STDERR

The message "No plugins added. Use `cordova plugin add <plugin>`." is printed to STDOUT when running the command "cordova plugin list" when there are no plugins installed.

It should be printed to STDERR instead to be consistent with other linux programs.

Ryans-Mac:MyApp ryan$ cordova plugin list 2>/dev/null
No plugins added. Use `cordova plugin add <plugin>`.

Ryans-Mac:MyApp ryan$ cordova plugin list 2>/dev/null | wc -l
1