chore(package): update eslint to version 6.8.0

Closes #46

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
     "@babel/preset-env": "^7.0.0",
     "@babel/register": "^7.0.0",
     "babel-preset-power-assert": "^3.0.0",
-    "eslint": "^5.0.0",
+    "eslint": "^6.8.0",
     "gitbook-cli": "^2.3.2",
     "gitbook-plugin-include-codeblock": "^3.0.0",
     "mocha": "^6.1.4",