Forecast: Do not display day if temperatureMin/Max DNE.

Some days do not have temperatureMax or temperatureMin in the API. This results in a NaN° being shown in our results (also, we can't make a graph with a NaN).
Merge pull request #337 from duckduckgo/jag/bug/forecast-NaN

Forecast: Do not display day if temperatureMin/Max DNE.