hotfix: no-cache cache-control for preview mode

Author: lindsaylevine

lib/templates/netlifyFunction.js

@@ -19,6 +19,8 @@ const callbackHandler = (callback) =>
       ].map((value) => String(value));
     });
 
+    response.multiValueHeaders["Cache-Control"] = ["no-cache"];
+
     // Invoke callback
     callback(argument, response);
   };