build: bump ICU from 54 to 55

[srl295]

node is using ICU 54 ( 2014-oct-06 ). Bump to 55 ( 2015-apr-08)

Note that ICU 56 is scheduled for 2015-oct ish.

( Parallel to nodejs/node-v0.x-archive#25790 )

[srl295]

see nodejs/node-v0.x-archive#25790

[jbergstroem]

Quick Q; what upstream fixes/functionality do we get?

[srl295]

@jbergstroem Current/updated time zone and locale data. Speed improvements in date formatting. icu4c 55 changelot / cldr 27 changelog.