Use Https for loading open sans
Use Https for loading open sans

This PR changes to using https for loading the font from google fonts.

I was getting a mixed content warning when loading this font:

```
Mixed Content: The page at
'https://example.com/dash/dashboard/' was loaded over
HTTPS, but requested an insecure stylesheet
'http://fonts.googleapis.com/css?family=Open+Sans:300,400,600,700'. This
request has been blocked; the content must be served over HTTPS.
```

talpor/django-dashing,talpor/django-dashing,talpor/django-dashing