fix escaping

{{cookiecutter.packer_name}}/packer.json

@@ -1,7 +1,10 @@
 {
   "variables": {
+    {% raw -%}
     "source_ami"     : "{{ env `SOURCE_AMI` }}",
+    {% endraw -%}
     "region"         : "{{ cookiecutter.aws_region }}",
+    {% raw -%}
     "aws_access_key" : "{{ env `AWS_ACCESS_KEY_ID` }}",
     "aws_secret_key" : "{{ env `AWS_SECRET_ACCESS_KEY` }}"
  },
@@ -29,6 +32,7 @@
       "source_ami"    : "{{user `source_ami`}}",
       "ssh_username"  : "ubuntu",
       "instance_type" : "m3.medium",
+    {% endraw -%}
       "ami_name"      : "{{cookiecutter.packer_name}}-{{timestamp}}",
       "tags"          : {
 		  "role"       : "{{cookiecutter.packer_name}}",