Fix plus sign in console

Not sure where to test this, it looks like middleware isn't covered in the current tests. If there's a way to do it, let me know.

Anyway, this patch allows you to add numbers in the console.

Previously:
```
>> 1+1
!! #<SyntaxError: /Users/milan/Projects/testapp/app/controllers/users_controller.rb:7: syntax error, unexpected tINTEGER, expecting end-of-input>
```

Now:
```
>> 1+1
=> 2
```

The explanation: The plus sign was getting lost when request.params were generated.