We had three JSON schema matchers:

1. `match_schema` - takes a data structure and a path to a schema file.
2. `match_response_schema` - takes a response object and a path to a
   schema file.
3. `according_to_schema` - chained matcher on `be_valid_json`, takes a
   schema literal.

The reason for this is that we wanted to operate on various axes:

1. Are we validating a parsed data structure, or a potentially-JSON
   string?
2. Are we providing a path to a schema file, or a literal data structure
   representing a schema?

Happily, the library we're using already solves problem 1 for us.
https://github.com/ruby-json-schema/json-schema#validation says:

> All methods take two arguments, which can be either a JSON string, a
> file containing JSON, or a Ruby object representing JSON data.

So we just needed to solve concern 2, and we handle that by assuming
that if the schema argument is a string, it's not a JSON string
representing the schema, but a path to a schema file.

To handle the chaining that `according_to_schema` had, we can just use
RSpec's `and` method:

    be_valid_json.and match_schema(build_info_payload_schema)