Update settings.py

Used os.env to get variables

Author: dmytrotsko

src/signal_documentation/settings.py

@@ -23,8 +23,8 @@
 from sentry_sdk.integrations.django import DjangoIntegration
 from sentry_sdk.integrations.redis import RedisIntegration
 
-EPIVIS_URL = "https://deploy-preview-36--cmu-delphi-epivis.netlify.app/"
-DATA_EXPORT_URL = "https://api.covidcast.cmu.edu/epidata/covidcast/csv"
+EPIVIS_URL = os.environ.get("EPIVIS_URL", "https://deploy-preview-36--cmu-delphi-epivis.netlify.app/")
+DATA_EXPORT_URL = os.environ.get("DATA_EXPORT_URL", "https://api.covidcast.cmu.edu/epidata/covidcast/csv")
 
 SENTRY_DSN = os.environ.get('SENTRY_DSN')
 if SENTRY_DSN: