Fix #17 Rake task to update corona stats

[coolbrg]

We can now update the corona stats by the following command.

rake update_corona_stats world="17,22,514:1,04,775:3,89,292" nepal="9:0:1"

It has updated the file _data/corona_stats.yml as:

---
np:
  world:
    confirmed: १७,२२,५१४
    deaths: १,०४,७७५
    recovered: ३,८९,२९२
  nepal:
    confirmed: ९
    deaths: ०
    recovered: १
en:
  world:
    confirmed: '17,22,514'
    deaths: '1,04,775'
    recovered: '3,89,292'
  nepal:
    confirmed: '9'
    deaths: '0'
    recovered: '1'