fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:hoek:20180212

Latest report for kelektiv/node.bcrypt.js:
https://snyk.io/test/github/kelektiv/node.bcrypt.js

Author: snyk-bot

package.json

@@ -30,7 +30,7 @@
   },
   "dependencies": {
     "nan": "2.8.0",
-    "node-pre-gyp": "0.6.39"
+    "node-pre-gyp": "0.7.0"
   },
   "devDependencies": {
     "nodeunit": "~0.9.1"