Check if a newer version is available

[clsource]

Add a version check to know if a newer mob.new version is available and recommend update it with mix archive.install hex mob_new.

Example:

https://github.com/phoenixframework/phoenix/blob/b6a4e31325197fae150096eadce93846dcfb58e5/installer/lib/mix/tasks/phx.new.ex#L547