Format .tfvars file as HashiCorp Config Language. (#3885)

* Format .tfvars file as HashiCorp Config Language.

* Add sample terraform.tfvars file to demonstrate HCL rendering.

lib/linguist/languages.yml

@@ -1692,6 +1692,7 @@ HCL:
   extensions:
   - ".hcl"
   - ".tf"
+  - ".tfvars"
   ace_mode: ruby
   codemirror_mode: ruby
   codemirror_mime_type: text/x-ruby

samples/HCL/terraform.tfvars

@@ -0,0 +1,58 @@
+# Terragrunt is a thin wrapper for Terraform that provides extra tools for working with multiple Terraform modules,
+# remote state, and locking: https://github.com/gruntwork-io/terragrunt
+terragrunt = {
+  # Configure Terragrunt to automatically store tfstate files in an S3 bucket
+  remote_state {
+    backend = "s3"
+    config {
+      encrypt        = true
+      bucket         = "acme-main-terraform-state"
+      key            = "${path_relative_to_include()}/terraform.tfstate"
+      region         = "us-east-1"
+      dynamodb_table = "terraform-locks"
+    }
+  }
+
+  # Configure Terragrunt to use common var files to help you keep often-repeated variables (e.g., account ID) DRY.
+  # Note that even though Terraform automatically pulls in terraform.tfvars, we include it explicitly at the end of the
+  # list to make sure its variables override anything in the common var files.
+  terraform {
+    extra_arguments "common_vars" {
+      commands = ["${get_terraform_commands_that_need_vars()}"]
+
+      optional_var_files = [
+        "${get_tfvars_dir()}/${find_in_parent_folders("account.tfvars", "skip-account-if-does-not-exist")}",
+        "${get_tfvars_dir()}/${find_in_parent_folders("region.tfvars", "skip-region-if-does-not-exist")}",
+        "${get_tfvars_dir()}/${find_in_parent_folders("env.tfvars", "skip-env-if-does-not-exist")}",
+        "${get_tfvars_dir()}/terraform.tfvars"
+      ]
+    }
+  }
+}
+
+key1 = "val1"
+key2 = 0
+key3 = 1
+key4 = true
+
+# Sample comments
+key5 = false
+
+key6 = ["hello", "from", "gruntwork.io"]
+
+key7 = {
+  key1 = "hello"
+  key2 = "from"
+  key3 = "gruntwork.io"
+}
+
+key8 = [
+  {
+    keyA = "hello"
+    keyB = "there"
+  },
+  {
+    keyA = "hello"
+    keyB = "there"
+  }
+]