update getting started docs to use a filter meaning they should stay up to date longer

website/source/intro/getting-started/build-image.html.md

@@ -55,7 +55,15 @@ briefly. Create a file `example.json` and fill it with the following contents:
     "access_key": "{{user `aws_access_key`}}",
     "secret_key": "{{user `aws_secret_key`}}",
     "region": "us-east-1",
-    "source_ami": "ami-fce3c696",
+    "source_ami_filter": {
+      "filters": {
+      "virtualization-type": "hvm",
+      "name": "*ubuntu-xenial-16.04-amd64-server-*",
+      "root-device-type": "ebs"
+      },
+      "owners": ["099720109477"],
+      "most_recent": true
+    },
     "instance_type": "t2.micro",
     "ssh_username": "ubuntu",
     "ami_name": "packer-example {{timestamp}}"