 Ruby 2.7 deprecation warning with middleware/error

Addressing issue #1992 via #2064 has fixed some of the warnings but not all of them, I am still seeing this:

```
/gems/rack-2.2.3/lib/rack/builder.rb:158: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/gems/grape-1.4.0/lib/grape/middleware/error.rb:30: warning: The called method `initialize' is defined here
```