Fix missing rdf-string dependency in core, Closes #131

Author: rubensworks

packages/core/package.json

@@ -43,6 +43,7 @@
     "mime": "^2.4.4",
     "n3": "^1.3.5",
     "negotiate": "^1.0.1",
+    "rdf-string": "^1.3.1",
     "q": "^1.4.1",
     "qejs": "^3.0.5",
     "request": "^2.88.2",