config.beta.js update backend_url to HTTPS

Now that the beta site is being served over HTTPS, pages which used the backend were not able to connect to it because the backend was being requested via HTTP. 
Update the config template to request the backend via HTTPS.

Mixed Content: The page at 'https://brcaexchange-prod.gi.ucsc.edu/releases' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'http://brcaexchange-prod.gi.ucsc.edu/backend/data/releases'. This request has been blocked; the content must be served over HTTPS.

deployment/site_settings/config.beta.js

@@ -5,7 +5,7 @@
         baseurl: '/',
         captcha_key: '', /* reCAPTCHA API key */
         maps_key: '', /* Google maps javascript API key */
-        backend_url: 'http://brcaexchange-prod.gi.ucsc.edu/backend',
+        backend_url: 'https://brcaexchange-prod.gi.ucsc.edu/backend',
         analytics: null,
         environment: 'beta'
     };