chore(package): update mocha to version 6.1.0

Closes #11

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "graphql": "^14.0.2",
     "graphql-relay": "^0.5.0",
     "istanbul": "^0.4.5",
-    "mocha": "^3.0.2",
+    "mocha": "^6.1.0",
     "multiline": "^2.0.0"
   }
 }