fix(package): update bignumber.js to version 8.0.2

Closes #5

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "tape": "^4.6.3"
   },
   "dependencies": {
-    "bignumber.js": "^4.0.4",
+    "bignumber.js": "^8.0.2",
     "murmurhash3": "^0.4.0"
   }
 }