Fixed advanced search subject and keyword subject -congresses, keyword I...

...EEE xplore keyword: increased have_at_most value

1) advanced search subject and keyword subject -congresses, keyword IEEE xplore keyword
     Failure/Error: resp.should have_at_most(8550).results
       expected at most 8550 results, got 8570
     # ./spec/advanced_search_spec.rb:113:in `block (4 levels) in <top (required)>'

@ndushay