initial ref transaction called with existing refs on init

Running `terraform init` after providing variables grants the following error
```
Error downloading modules: Error loading modules: error downloading 'https://github.com/ulamlabs/terraform-aws-rabbitmq?ref=v3.0.0': /usr/bin/git exited with 128: Cloning into '.terraform/modules/092ebc75691ed8de2f41a34a62b78538'...
fatal: BUG: initial ref transaction called with existing refs
```