Use splat + join synatx on s3_bucket arn (#2)

* Use splat + join synatx on s3_bucket arn

As we are using a count on this resource and are currently getting
the following warning message:

```
Warning: output "s3_bucket_arn": must use splat syntax to access aws_s3_bucket.default attribute "arn", because it has "count" set; use aws_s3_bucket.default.*.arn to obtain a list of the attributes across all instances
```

* docs fix for lint check to pass

README.md

@@ -75,7 +75,6 @@ Available targets:
   lint                                Lint terraform code
 
 ```
-
 ## Inputs
 
 | Name | Description | Type | Default | Required |

docs/terraform.md

@@ -1,4 +1,3 @@
-
 ## Inputs
 
 | Name | Description | Type | Default | Required |

outputs.tf

@@ -51,6 +51,6 @@ output "secret_access_key" {
 }
 
 output "s3_bucket_arn" {
-  value       = "${aws_s3_bucket.default.arn}"
+  value       = "${join("", aws_s3_bucket.default.*.arn)}"
   description = "S3 bucket ARN"
 }