use 8 threads for benchmarks

benchmarks/run

@@ -9,7 +9,7 @@ sleep 2
 wrk 'http://localhost:3333/?foo[bar]=baz' \
   -d 3 \
   -c 50 \
-  -t 4 \
+  -t 8 \
   | grep 'Requests/sec' \
   | awk '{ print "  " $2 }'