Fix #251

[johannesegger]

I also changed the type of previousReleases to be a list to avoid multiple enumerations.

I'm not sure if I also should create some tests. Currently there is no test project for the "Update" project. All tests seem to test functionality on the "customer"-side.

[willdean]

@eggapauli I would be happy to help you create some more tests if Paul agrees they're worthwhile - even a lot of the existing Squirrel tests are disabled/failing on my machine.

Maybe it the code you fixed could come out of update program.cs into Squirrel.dll, where it would be easier to test with the existing framework, without needing a new project.

[johannesegger]

@willdean I agree that tasks like releasifying should not be in Update.exe for several reasons. I would prefer not to include it in Squirrel.dll, but create a separate project for it. Then we could use it for example on a build server to releasify apps without having to start a separate process (i.e. Squirrel.exe). But that's not the topic of this PR anyway, so let's not discuss this here.

[anaisbetts]

Thanks! 👍