[#69915642] Bump vCloud Core version to 0.0.12

Bump vCloud Core to version 0.0.12, which fixes an issue where tasks
that would show a progress bar fall over which this error message:

```
undefined method `<' for nil:NilClass
```
Bump Gem version to 0.2.3
Merge pull request #44 from alphagov/bump-vcloud-core

[#69915642] Bump vCloud Core version to 0.0.12 and vcloud-edge_gateway version to 0.2.3