Fix build warnings in node 8

[deepakrkris]

• Update Nan version in package.json to 2.6.2

• Use Nan::CallAsConstructor instead of v8::Object::CallAsConstructor

#53

[deepakrkris]

@Southern please review

[tanuck]

I think the versions list for travis should be updated before merging this, just to be sure of backwards compatibility.

[deepakrkris]

@tanuck thank you for your observation , do you want to update the semver to 0.3.3 before merging this change ?

[deepakrkris]

@Southern @tanuck please review and comment

[tanuck]

@deepakrkris sorry but I don't have the ability to merge. So you'll have to wait on @Southern

[deepakrkris]

@Southern is this PR good to merge ? or do you want to close this , since it has been more than 8 months

[gzurbach]

Would like to see this merged as well.

[mbwhite]

Ditto the merge of this one; we've found it raises lots of questions with end users to see the warnings go past.

[deepakrkris]

closing as this was fixed in #74