* Upgrade to terraform-plugin-sdk
After following the [guide](https://www.terraform.io/docs/extend/plugin-sdk.html#using-tf-sdk-migrator)
Check
```
▶ GO111MODULE=on tf-sdk-migrator check
Checking Go runtime version ...
Go version 1.12.10: OK.
Checking whether provider uses Go modules...
Go modules in use: OK.
Checking version of github.com/hashicorp/terraform-plugin-sdk to determine if provider was already migrated...
Checking version of github.com/hashicorp/terraform used in provider...
Terraform version 0.12.8: OK.
Checking whether provider uses deprecated SDK packages or identifiers...
No imports of deprecated SDK packages or identifiers: OK.
All constraints satisfied. Provider can be migrated to the new SDK.
```
Migrate
```
▶ GO111MODULE=on tf-sdk-migrator migrate
Checking Go runtime version ...
Go version 1.12.10: OK.
Checking whether provider uses Go modules...
Go modules in use: OK.
Checking version of github.com/hashicorp/terraform-plugin-sdk to determine if provider was already migrated...
Checking version of github.com/hashicorp/terraform used in provider...
Terraform version 0.12.8: OK.
Checking whether provider uses deprecated SDK packages or identifiers...
No imports of deprecated SDK packages or identifiers: OK.
All constraints satisfied. Provider can be migrated to the new SDK.
Rewriting provider go.mod file...
Rewriting SDK package imports...
Running `go mod tidy`...
Success! Provider is migrated to github.com/hashicorp/terraform-plugin-sdk v1.1.0.
It looks like this provider vendors dependencies. Don't forget to run `go mod vendor`.
Make sure to review all changes and run all tests.
```
* Fix build under go 1.13.x.
655147c103