fix(package): update openzeppelin-solidity to version 3.0.1

Closes #86

Author: greenkeeper[bot]

package.json

@@ -91,7 +91,7 @@
     "dotenv": "^6.1.0",
     "lodash": "^4.17.11",
     "nanoid": "^2.0.1",
-    "openzeppelin-solidity": "2.0.0",
+    "openzeppelin-solidity": "3.0.1",
     "sha3": "^1.2.2",
     "solidity-bytes-utils": "0.0.5",
     "truffle-flattener": "^1.2.8"