dashboard: remove protocol from google fonts links so they work with https

When an etcd cluster is secured with client certs, the dashboard will fail to load fonts and show the following error in the developer console:
```
[blocked] The page at 'https://etcd:4001/mod/dashboard/' was loaded over HTTPS, but ran insecure content from 'http://fonts.googleapis.com/css?family=Source+Sans+Pro:200,300,400,400italic,600,700,900': this content should also be loaded over HTTPS.
 54.215.11.69/:10
[blocked] The page at 'https://etcd:4001/mod/dashboard/' was loaded over HTTPS, but ran insecure content from 'http://fonts.googleapis.com/css?family=Source+Code+Pro:400,500,600,700': this content should also be loaded over HTTPS.
```
Removing the protocols from the links will allow them to be loaded over HTTP or HTTPS.