Scrub keys from hash arguments

[aabes]

This is an attempt to filter out large elements from a body of a POST message, that rollbar is attempting to post in the content of an error.

The environment is a rack app (running in puma). A post request with a structure similar to below causes an error -

 {
   "foo": 1,
   "blob": "very large data"
 }
 

The rollbar configuration has:

config.scrub_fields = [:blob]

but despite that, blob is included in the payload (and posting the error fails due to size).

This PR ensures that the hash keys included in the scrub_fields are excluded from the payload.

Does this ring right?

[rokob]

I am going to close this because #567 which was just merged solves this problem.

[aabes]

@rokob - what version of the gem will this equivalent PR be available in (i.e. I want to switch away from my fork back to a supported version).