input: Write a python function to serialize a dictionary using the `json` library.
  assert serialize_dict({"name": "John", "age": 30}) == '{"name": "John", "age": 30}'
  assert serialize_dict({"a": 1, "b": 2, "c": 3}) == '{"a": 1, "b": 2, "c": 3}'
  assert serialize_dict({}) == '{}'
output: def serialize_dict(d):
      import json
      return json.dumps(d)