Add node 6.12.3, remove node 6.12.2
Add node 6.12.3, remove node 6.12.2

source url: https://nodejs.org/dist/v6.12.3/node-v6.12.3.tar.gz
source sha256: 088788d1c887309f8650730908dbf6f09140077a8aaf582021af4bef2a6d6b84

[#154004430]

cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack