Don't specify gem versions

Don't specify the versions that this meta-gem installs.

By not specifying the versions, new users of vCloud Tools will install
the latest available versions of the tools and we avoid having to
increment the versions each time a gem is updated.
Add vCloud Tools Tester gem development dependency

Add the vCloud Tools Tester gem as a development dependency now that
this gem has been released.
Version 1.0.0

Bump version to 1.0.0 now that we have included the vCloud Tools Tester
gem and we now depend on the latest available versions of the vCloud
Tools gems.

Update the CHANGELOG accordingly.
Merge pull request #191 from alphagov/dont-specify-versions

[Fixes #70438882] Don't pin gem versions