chore(package): update eslint to version 6.0.1

Closes #79

Author: greenkeeper[bot]

package.json

@@ -58,7 +58,7 @@
     "babel-register": "^6.18.0",
     "chai": "^4.0.2",
     "chai-string": "^1.3.0",
-    "eslint": "^4.1.0",
+    "eslint": "^6.0.1",
     "eslint-plugin-flowtype": "^2.29.2",
     "flow-bin": "^0.61.0",
     "mocha": "^5.0.0",