Fix q20 sql typo in benchmarks (#409)

Author: r4ntix

benchmarks/queries/q20.sql

@@ -28,10 +28,10 @@ where
                     l_partkey = ps_partkey
               and l_suppkey = ps_suppkey
               and l_shipdate >= date '1994-01-01'
-              and l_shipdate < 'date 1994-01-01' + interval '1' year
+              and l_shipdate < date '1994-01-01' + interval '1' year
         )
     )
   and s_nationkey = n_nationkey
   and n_name = 'CANADA'
 order by
-    s_name;
+    s_name;