Use example_runtime instead of total runtime

This fixes the issue where < 10 examples in profile showed less than 
100% total time.

src/spectator/profile.cr

@@ -36,7 +36,7 @@ module Spectator
       results = report.compact_map(&.as?(FinishedResult))
       sorted_results = results.sort_by(&.elapsed)
       slowest = sorted_results.last(size).reverse
-      self.new(slowest, report.runtime)
+      self.new(slowest, report.example_runtime)
     end
   end
 end