chore: upgrade dependencies

Author: Matt Lewis

package.json

@@ -57,7 +57,7 @@
     "@types/chai": "^4.0.0",
     "@types/highlight.js": "^9.1.9",
     "@types/mocha": "^2.2.41",
-    "@types/node": "^7.0.29",
+    "@types/node": "^8.0.1",
     "@types/rrule": "^2.1.3",
     "@types/sinon": "^2.2.2",
     "@types/sinon-chai": "^2.7.26",