Fix Ruby 2.7 deprecation in helper.rb.

Author: connorshea

lib/sprockets/rails/helper.rb

@@ -353,7 +353,7 @@ def find_debug_asset(path)
 
         private
           def find_asset(path, options = {})
-            @env[path, options]
+            @env[path, **options]
           end
 
           def precompiled?(path)