Use updated birth data

[swo]

• Right now, natality data are tracked in the repo
• There are two sources for birth data:
  • WONDER API, which has final data query, and get birth data from the API
  • Provisional data: https://data.cdc.gov/resource/hmz2-vwda.json, which is already in scripts/get_birth_data.py
• We'll want to stitch the final and provisional data together (unless it's already done somewhere)
• WONDER API includes some other kinds of characteristics, like birth weight
• data.cdc.gov API is easier than WONDER