chore(package): update solhint to version 2.1.0

Closes #85

Author: greenkeeper[bot]

package.json

@@ -78,7 +78,7 @@
     "mocha-lcov-reporter": "^1.3.0",
     "semver": "^5.5.1",
     "solc": "^0.4.24",
-    "solhint": "^1.5.0",
+    "solhint": "^2.1.0",
     "solidity-coverage": "^0.5.5",
     "solium": "^1.1.8",
     "truffle": "^4.1.13",