Fix for building on node v10

[No9]

This patch implements the Nan wrapper for New Instance Test ran against v6 and v10 of node on FreeBSD 12 Current

> dtrace-provider@0.8.6 test /usr/home/anton/code/node-dtrace-provider
> tap test/*.test.js

ok test/32probe-char.test.js .......................... 35/35
ok test/32probe.test.js ............................. 531/531
ok test/add-probes.test.js ............................ 49/49
ok test/args-after-cb-1.test.js ......................... 5/5
ok test/args-after-cb-2.test.js ......................... 5/5
ok test/basic.test.js ................................... 4/4
ok test/create-destroy.test.js ........................ 13/13
ok test/disambiguation.test.js .......................... 7/7
ok test/enabled-disabled.test.js ...................... 13/13
ok test/enabledagain.test.js ............................ 6/6
ok test/fewer-args-json.test.js ......................... 4/4
ok test/fewer-args.test.js .............................. 5/5
ok test/gc-provider.test.js ............................. 3/3
ok test/gc.test.js ...................................... 3/3
ok test/json-args.test.js ............................... 5/5
ok test/more-args.test.js ............................... 4/4
ok test/multiple-json-args.test.js ...................... 3/3
ok test/notenabled.test.js .............................. 2/2
total ............................................... 697/697

ok

[matttrawicki]

👍 Thank you @No9

[melloc]

Merged as 06f8a691. Thanks @No9! I'm going to also fix #120, and then release dtrace-provider@0.8.7 with these changes.