support nodejs 6.x (update nan, use node-gyp)

[dankang]

• update nan version (2.1.0 => 2.3.5)
• use node-gyp instead of pangyp(deprecated)
• tested on nodejs 4.4.5 & 6.2.2

[dankang]

@kuno
Right now, I can only check Travis CI build results.
If you give me the access permission for AppVeyor, Wercker.. I will fix build failure.

[fmasuhr]

@kuno is there any chance to get this merged? There are multiple security issues in the pangyp dependencies since it is deprecated.

[chetverikov]

+1

[diversario]

node v6 has moved into active LTS mode and a lot of people can't upgrade their projects (myself included) because we have a dependency on this package. This PR really needs to be rolled in at least to make it possible to upgrade.

[luigizuccarelli]

@kuno - what is the status on this ?. We have an urgent need to have this mergerd due to nsp checks

 minimatch   2.0.10      >=3.0.2                      fh-messaging@3.0.2-BUILD-NUMBER > geoip@0.6.1 > pangyp@2.3.3 > glob@4.3.5 > minimatch@2.0.10   https://nodesecurity.io/advisories/118 
 minimatch   2.0.10      >=3.0.2                      fh-messaging@3.0.2-BUILD-NUMBER > geoip@0.6.1 > pangyp@2.3.3 > minimatch@2.0.10                https://nodesecurity.io/advisories/118 

[CaptEmulation]

I needed this so I created @captemulation/geoip@0.6.2