Fix benchmarks

[TimothyGu]

Addresses @jkummerow and @hashseed's comments on the blog post (@jkummerow,
@hashseed).

How were the charts produced? I'd like to update them as well.

• numbers.js

  On Node.js v8.2.1 with V8 5.8:

  sum small x 21,061 ops/sec ±1.68% (88 runs sampled)
  from small to big x 14,684 ops/sec ±0.50% (91 runs sampled)
  all big x 9,515 ops/sec ±0.46% (90 runs sampled)
  

  On Node.js v9.0.0-v8-canary20170724c045f1f8dc with V8 6.2.4:

  sum small x 16,438 ops/sec ±1.40% (86 runs sampled)
  from small to big x 14,751 ops/sec ±0.67% (90 runs sampled)
  all big x 11,993 ops/sec ±5.12% (84 runs sampled)
  

  Compare:

• object-creation.js

  Node.js v8.2.1 with V8 5.8:

  literal x 28,455,810 ops/sec ±1.19% (83 runs sampled)
  class x 21,993,317 ops/sec ±1.13% (86 runs sampled)
  constructor x 28,093,899 ops/sec ±0.73% (82 runs sampled)
  

  Node.js v9.0.0-v8-canary20170724c045f1f8dc with V8 6.2.4:

  literal x 31,861,977 ops/sec ±0.88% (86 runs sampled)
  class x 32,265,246 ops/sec ±0.65% (90 runs sampled)
  constructor x 32,120,661 ops/sec ±0.99% (87 runs sampled)
  

  Compare:

Refs: nodejs/CTC#155 (comment)

[mcollina]

The charts are produced from the attached google spreadsheet: https://docs.google.com/spreadsheets/d/1mDt4jDpN_Am7uckBbnxltjROI9hSu6crf9tOa2YnSog/edit?usp=sharing.

I'll rerun the benchmarks on all platforms and update the results.