Update error: Code signature did not pass validation: code object is not signed at all
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### Description

When updating the app from v0.2.10, the update fails with the following error:

![screen shot 2017-11-06 at 8 30 58 am](https://user-images.githubusercontent.com/297461/32443523-4939b0a8-c2cd-11e7-9db6-7532f379e0fe.png)


### Version

**Kactus version:** v0.2.10

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**OS version:** 10.13.2

### Steps to Reproduce

1. Open "about kactus"
1. Click "check for update"


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**Expected behavior:** The app updates to the new version

**Actual behavior:** Above error is displayed

**Reproduces how often:** 100%

### Logs

```
2017-11-06T13:25:59.316Z - info: [ui] launching: 0.2.10 (Mac OS 10.13.2)
2017-11-06T13:25:59.598Z - info: [ui] Stats reported.
2017-11-06T13:26:09.907Z - error: [ui] Error checking for updates
Error: Code signature at URL file:///Users/alampros/Library/Caches/io.kactus.KactusClient.ShipIt/update.eNzIl8v/Kactus.app/ did not pass validation: code object is not signed at all
2017-11-06T13:29:30.605Z - error: [ui] Error checking for updates
Error: Code signature at URL file:///Users/alampros/Library/Caches/io.kactus.KactusClient.ShipIt/update.CekZu1r/Kactus.app/ did not pass validation: code object is not signed at all
2017-11-06T13:29:57.360Z - error: [ui] Error checking for updates
Error: Code signature at URL file:///Users/alampros/Library/Caches/io.kactus.KactusClient.ShipIt/update.Fs4NQ3I/Kactus.app/ did not pass validation: code object is not signed at all
2017-11-06T13:30:05.455Z - info: [ui] launching: 0.2.10 (Mac OS 10.13.2)
2017-11-06T13:30:14.946Z - error: [ui] Error checking for updates
Error: Code signature at URL file:///Users/alampros/Library/Caches/io.kactus.KactusClient.ShipIt/update.9Aw9keB/Kactus.app/ did not pass validation: code object is not signed at all
2017-11-06T13:30:53.678Z - error: [ui] Error checking for updates
Error: Code signature at URL file:///Users/alampros/Library/Caches/io.kactus.KactusClient.ShipIt/update.iFMYTg4/Kactus.app/ did not pass validation: code object is not signed at all

```

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