fix(package): update nanoid to version 3.1.8

Closes #98

Author: greenkeeper[bot]

package.json

@@ -90,7 +90,7 @@
     "chai-arrays": "^2.0.0",
     "dotenv": "^6.1.0",
     "lodash": "^4.17.11",
-    "nanoid": "^2.0.1",
+    "nanoid": "^3.1.8",
     "openzeppelin-solidity": "2.0.0",
     "sha3": "^1.2.2",
     "solidity-bytes-utils": "0.0.5",