Gather `seq_scan` from `pg_stat_user_tables` per table

Closes #13

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-monitor (1.0.0)
+    gitlab-monitor (1.1.0)
       pg (~> 0.18.4)
       quantile (~> 0.2.0)
       redis-namespace (~> 1.5.2)

lib/gitlab_monitor/database/tuple_stats.rb

@@ -5,7 +5,7 @@ module GitLab
       #
       # It takes a connection string (e.g. "dbname=test port=5432")
       class TupleStatsCollector < Base
-        COLUMNS = %w(relname seq_tup_read idx_tup_fetch n_tup_ins n_tup_upd n_tup_del n_tup_hot_upd n_dead_tup)
+        COLUMNS = %w(relname seq_tup_read idx_tup_fetch n_tup_ins n_tup_upd n_tup_del n_tup_hot_upd n_dead_tup seq_scan)
                   .join(",")
         QUERY   = <<-SQL.freeze
           SELECT #{COLUMNS}

lib/gitlab_monitor/version.rb

 module GitLab
   module Monitor
-    VERSION = "1.0.0".freeze
+    VERSION = "1.1.0".freeze
   end
 end