Update bignum in dev dependencies

Author: fanatid

package.json

@@ -57,7 +57,7 @@
     "safe-buffer": "^5.1.0"
   },
   "devDependencies": {
-    "bignum": "^0.12.5",
+    "bignum": "^0.13.0",
     "browserify": "^14.4.0",
     "karma": "^1.3.0",
     "karma-browserify": "^5.0.4",