Recognize JSON API response as JSON

Make sure we recognize `application/vnd.api+json` as JSON to pretty format it
using `response_body_formatter`

Author: timurvafin

lib/rspec_api_documentation/configuration.rb

@@ -110,7 +110,7 @@ def self.add_setting(name, opts = {})
     # See RspecApiDocumentation::DSL::Endpoint#do_request
     add_setting :response_body_formatter, default: Proc.new { |_, _|
       Proc.new do |content_type, response_body|
-        if content_type =~ /application\/json/
+        if content_type =~ /application\/.*json/
           JSON.pretty_generate(JSON.parse(response_body))
         else
           response_body