Move boom to versions, fix failure to launch

Boom2 is out, so to update the main cask, this is the previous (boom1) version. 
This particular application, when it launches, if it launches from a directory with a file called ".DMG_Background_new.png", then it will refuse to launch...instead, telling the user to move the file from the disk image.  Apparently, that is the way that the company has chosen to implement the "Am I running from a disk image" check.

Since all files are copied from the disk image to staged_path, (including the disk image background png file), then the application "thinks" that it is still running from the disk image.

I agree - it is an issue with the way that the application is coded...but without this fix, the cask is completely useless.