Update rdflib to 0.16.2.

Fixes #497.

Author: RubenVerborgh

package.json

@@ -56,7 +56,7 @@
     "node-forge": "^0.6.38",
     "nodemailer": "^3.1.4",
     "nomnom": "^1.8.1",
-    "rdflib": "^0.15.0",
+    "rdflib": "^0.16.2",
     "recursive-readdir": "^2.1.0",
     "request": "^2.72.0",
     "rimraf": "^2.5.0",