Reduce number of iterations of the nbody benchmark

It was unnecessarily long.

Author: Kobzol

collector/runtime-benchmarks/nbody/src/main.rs

@@ -7,13 +7,13 @@ mod nbody;
 
 fn main() {
     run_benchmark_group(|group| {
-        group.register_benchmark("nbody_10k", || {
-            let mut nbody_10k = nbody::init(10000);
+        group.register_benchmark("nbody_5k", || {
+            let mut nbody = nbody::init(5000);
             || {
                 for _ in 0..10 {
-                    nbody_10k = nbody::compute_forces(nbody_10k);
+                    nbody = nbody::compute_forces(nbody);
                 }
-                nbody_10k
+                nbody
             }
         });
     });