Make metadata requests use the cached endpoint automatically

The overhead for the non-cached endpoint is substantial.

Author: capnrefsmmat

src/client/delphi_epidata.R

@@ -524,7 +524,7 @@ Epidata <- (function() {
 
   # Fetch Delphi's COVID-19 Surveillance Streams metadata
   covidcast_meta <- function() {
-    return(.request(list(source='covidcast_meta')))
+    return(.request(list(source='covidcast_meta', cached='true')))
   }
 
   # Export the public methods

src/client/delphi_epidata.py

@@ -563,4 +563,4 @@ def covidcast(data_source, signal, time_type, geo_type, time_values, geo_value):
   @staticmethod
   def covidcast_meta():
     """Fetch Delphi's COVID-19 Surveillance Streams metadata"""
-    return Epidata._request({'source': 'covidcast_meta'})
+    return Epidata._request({'source': 'covidcast_meta', 'cached': 'true'})