I just downloaded 0.3.2 on my Mac, and it worked fine. I'm on 10.11.4. What version OS X are you on?
I've had the error in the past with older versions of PhoneGap Desktop -- worst case, you can use this command to get it started:
$ open /Applications/PhoneGap.app/Contents/MacOS/Electron
I'm on 10.10.5 and just tried your suggestion via terminal: same result. Starts to launch and then stops with same error message.
Kept searching and found it's an OSX security issue (thanks to a similar post that leads to link below).
Need to allow non-store apps to launch.
So, I'm up and running...
Another solution is to right click the app in the Application folder and choose open. That way you are not allowing every non-store-app to launch.