Only attempt to sweep the cache when cache sweeping is enabled

This mirrors code in the railtie that effectively enables cache sweeping
only in development unless otherwise configured.

Author: gaffneyc

lib/propshaft/server.rb

@@ -47,6 +47,8 @@ def extract_path_and_digest(env)
     end
 
     def execute_cache_sweeper_if_updated
-      @assembly.load_path.cache_sweeper.execute_if_updated
+      if @assembly.config.sweep_cache
+        @assembly.load_path.cache_sweeper.execute_if_updated
+      end
     end
 end