Require explicitly ActiveSupport Hash::Keys

Why:
Fixes error when running specs `bundle exec (/home/m/.rbenv/versions/3.1.0/bin/rspec)
bundle exec rspec spec/dsl_spec.rb`
```
NoMethodError:
undefined method `stringify_keys for {:name=>"Friday Order"}:Hash
...
dsl/endpoint.rb:171:in `block in extra_params
```

Author: keram

lib/rspec_api_documentation.rb

@@ -3,6 +3,7 @@
 require 'active_support/core_ext/array/extract_options'
 require 'active_support/core_ext/hash/conversions'
 require 'active_support/core_ext/hash/deep_merge'
+require 'active_support/core_ext/hash/keys'
 require 'cgi'
 require 'json'