update nan dependency to 1.6.2+
update nan dependency to 1.6.2+

This is required to build crypt3 under io.js

rolandpoulter/node-crypt3,sendanor/node-crypt3,sendanor/node-crypt3,rolandpoulter/node-crypt3,sendanor/node-crypt3,rolandpoulter/node-crypt3,rolandpoulter/node-crypt3