deps: upgrade libuv to 1.7.1

PR-URL: nodejs#2310
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

2015-08-19 io.js v3.1.0 Release

2015-08-04 io.js v3.0.0 Release

2015-08-03 io.js v3.0.0 RC 7

2015-07-30 io.js v3.0.0 RC 6

2015-07-28 io.js v2.5.0 Release

2015-07-24 io.js v3.0.0 RC 5

2015-07-22 io.js v3.0.0 RC 4

doc: Add notes for using @@toStringTag

2015-07-17 io.js v2.4.0 Release