Correct CHANGELOG release date for version 3.2.0

This release happened in April rather than May according to the Git
commit (and we're still in April at the time of writing).
[#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
```
Merge pull request #64 from alphagov/bump-core-version

[#69915642] Bump vCloud Core version to 0.0.12