Update benchmarks

[dead-claudia]

The benchmarks here are fairly out of date now (1 1/2 years at this point). Also, V8 has made some drastic performance improvements to their Promise implementation recently, so their performance is close to on par with Bluebird's now. The benchmarks really need updated.

[petkaantonov]

updated

note that latest node is using v8 5.5 so those improvements are still not reflected

[dead-claudia]

@petkaantonov Chrome is using 5.8 now, so they have the latest optimizations. The next major Node release is also going to use either that or 5.7, so they're going to have them, too. So when that happens (late this April), you should be able to update the benchmark again with faster numbers.