hubolib: Make the site benchmark output more compact

hubolib: Make the site benchmark output more compact

So you can do and get:

```
▶ ./benchSite.sh "YAML,num_pages=10"
Running with BenchmarkSiteBuilding/YAML,num_pages=10
BenchmarkSiteBuilding/YAML,num_pages=10-4                 1000       1611261 ns/op      730749 B/op        6458 allocs/op
PASS
ok      github.com/spf13/hugo/hugolib    8.168s
```