Bump ubuntu_unused_kernels to 0.2.0
Bump ubuntu_unused_kernels to 0.2.0

Which will keep the last two kernels instead of one:

- https://github.com/gds-operations/ubuntu_unused_kernels/pull/3

Depends on this PR being merged:

- https://github.com/gds-operations/ubuntu_unused_kernels/pull/4

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet