Ansible Jinja Error

ansible.yml

  - name: Push the conf
    template: src=./templates/conf.json.j2 dest=~/conf.json.j2 owner=$ansible_ssh_user mode=0600

conf.json.j2

#jinja2:variable_start_string:'[%' , variable_end_string:'%]'
{
  "key": [
    {
      "path": "[% hostname %]/{{ timestamp }}-{{ filename }}"
    }
  ]
}

error.py

fatal: [<IP>] => Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/ansible/runner/__init__.py", line 394, in _executor
    exec_rc = self._executor_internal(host, new_stdin)
  File "/usr/local/lib/python2.7/site-packages/ansible/runner/__init__.py", line 485, in _executor_internal
    return self._executor_internal_inner(host, self.module_name, self.module_args, inject, port, complex_args=complex_args)
  File "/usr/local/lib/python2.7/site-packages/ansible/runner/__init__.py", line 685, in _executor_internal_inner
    result = handler.run(conn, tmp, module_name, module_args, inject, complex_args)
  File "/usr/local/lib/python2.7/site-packages/ansible/runner/action_plugins/template.py", line 91, in run
    local_md5 = utils.md5s(resultant)
  File "/usr/local/lib/python2.7/site-packages/ansible/utils/__init__.py", line 523, in md5s
    digest.update(data)
TypeError: must be string or buffer, not dict