Upped have_at_most limits

@ndushay 
1) advanced search subject and keyword subject -congresses, keyword IEEE xplore keyword
     Failure/Error: resp.should have_at_most(8500).results
       expected at most 8500 results, got 8513
     # ./spec/advanced_search_spec.rb:113:in `block (4 levels) in <top (required)>'

  2) advanced search subject and keyword subject -congresses, keyword IEEE xplore subject NOT congresses and keyword
     Failure/Error: resp.should have_at_most(1450).results
       expected at most 1450 results, got 1494
     # ./spec/advanced_search_spec.rb:119:in `block (4 levels) in <top (required)>'