chore(package): update bn.js to version 4.11.6

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -28,7 +28,7 @@
   "author": "Andrey Sidorov <[email protected]>",
   "license": "MIT",
   "dependencies": {
-    "bn.js": "4.11.4",
+    "bn.js": "4.11.6",
     "cardinal": "0.7.0",
     "double-ended-queue": "2.1.0-0",
     "named-placeholders": "1.1.1",