Add node 6.12.1, remove node 6.11.5
Add node 6.12.1, remove node 6.11.5

source url: https://nodejs.org/dist/v6.12.1/node-v6.12.1.tar.gz
source sha256: 818b7b69e065c76f6bf505425ec7415930a870b3c00c8d27be19a1829ed2a913

[#153407348]

cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack,cloudfoundry/nodejs-buildpack