Update logmeinignition.rb

The current Homepage states:

> Looking for Ignition for Mac?
> Now it's called the LogMeIn Client desktop app

And links to a new homepage. I've updated the cask to reflect this change.

The `.dmg` is still called `LogMeInIgnition.dmg` but the app is now named `LogMeIn Client.app`. I've renamed the the app in the link stanza.

However, I'm not sure if the cask should be renamed or not.