Added "snow" to OpenWeatherMapOneCallDailyData.

[timrosskamp]

Make sure all boxes are checked (add x inside the brackets) when you submit your contribution, remove this sentence before doing so.

• [x] This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• [x] I have thoroughly tested my contribution.
• [ ] Should this code require changes to documentation I will contribute those to https://github.com/ThingPulse/docs.

This PR is a small change to the One Call API. Currently only the "rain" key will be parsed in the daily forecast, although OWM also provides a "snow" key where available.

I have tested the change in a project of mine and it was working well. The change is small but I'm not entirely sure there are no side effects to my contribution.

[marcelstoer]

Thank you!