Merge pull request SimplePEG#33 from SimplePEG/greenkeeper/eslint-6.0.0

Update eslint to the latest version 🚀

Author: obenjiro

package.json

@@ -31,7 +31,7 @@
   "devDependencies": {
     "chai": "^4.1.0",
     "coveralls": "^3.0.0",
-    "eslint": "^5.0.0",
+    "eslint": "^6.0.0",
     "istanbul": "^0.4.4",
     "mocha": "^5.0.0",
     "mocha-lcov-reporter": "^1.2.0",