tests/resource/aws_sns_sms_preferences: Fix Terraform 0.12 syntax
tests/resource/aws_sns_sms_preferences: Fix Terraform 0.12 syntax

These changes are backwards compatible with Terraform 0.11.

Previous output from Terraform 0.12 acceptance testing:

```
--- FAIL: TestAccAWSSNSSMSPreferences (9.10s)
    --- FAIL: TestAccAWSSNSSMSPreferences/deliveryRole (0.46s)
        testing.go:568: Step 0 error: /opt/teamcity-agent/temp/buildTmp/tf-test818181650/main.tf:41,76-77: Missing newline after argument; An argument definition must end with a newline.
    --- PASS: TestAccAWSSNSSMSPreferences/empty (3.95s)
    --- FAIL: TestAccAWSSNSSMSPreferences/almostAll (0.37s)
        testing.go:568: Step 0 error: /opt/teamcity-agent/temp/buildTmp/tf-test655623523/main.tf:3,27-28: Missing newline after argument; An argument definition must end with a newline.
    --- PASS: TestAccAWSSNSSMSPreferences/defaultSMSType (4.32s)
```

Output from Terraform 0.12 acceptance testing:

```
--- PASS: TestAccAWSSNSSMSPreferences (38.38s)
    --- PASS: TestAccAWSSNSSMSPreferences/empty (10.32s)
    --- PASS: TestAccAWSSNSSMSPreferences/almostAll (8.75s)
    --- PASS: TestAccAWSSNSSMSPreferences/defaultSMSType (9.64s)
    --- PASS: TestAccAWSSNSSMSPreferences/deliveryRole (9.67s)
```

kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws