Fix test to work with more versions of our dependencies.
Fix test to work with more versions of our dependencies.

We get various response headers based, I believe on version of Rack installed. The exact values of these headers are not under test here, so this is ok.

tmk-kwmr/rspec_api_doc_test,shhavel/rspec_api_documentation,jramos/rspec_api_documentation,tmk-kwmr/rspec_api_doc_test,shhavel/rspec_api_documentation,schmierkov/rspec_api_documentation,stefsava/rspec_api_documentation,cover/rspec_api_documentation,shhavel/rspec_api_documentation,engineyard/rspec_api_documentation,cover/rspec_api_documentation,jramos/rspec_api_documentation,schmierkov/rspec_api_documentation,stefsava/rspec_api_documentation,cover/rspec_api_documentation,saisai/rspec_api_documentation,zipmark/rspec_api_documentation,schmierkov/rspec_api_documentation,saisai/rspec_api_documentation,engineyard/rspec_api_documentation,stefsava/rspec_api_documentation,jramos/rspec_api_documentation,zipmark/rspec_api_documentation,engineyard/rspec_api_documentation,saisai/rspec_api_documentation,zipmark/rspec_api_documentation