chore(package): update mocha to version 6.1.3

Closes #29

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
     "chai": "^4.1.2",
     "coveralls": "^3.0.0",
     "istanbul": "^0.4.5",
-    "mocha": "^5.0.0",
+    "mocha": "^6.1.3",
     "n3": "^0.8.5",
     "random-access-memory": "^3.0.0",
     "standard": "^12.0.0",