Fix format of nanobench result

Column of samples is too wide. This makes config is not align with the
'config' title. Pad 'samples' tilte with some whitespaces to fix this
issue.

BUG=skia:
R=mtklein@google.com

Author: qiankun.miao@intel.com

Review URL: https://codereview.chromium.org/549153005
1 file changed