fix: upgrade eslint from 6.6.0 to 6.8.0

Snyk has created this PR to upgrade eslint from 6.6.0 to 6.8.0.

See this package in NPM:
https://www.npmjs.com/package/eslint

See this project in Snyk:
https://app.snyk.io/org/nodeshift-agg/project/ae73c67c-3bc9-47ee-9188-3c078ef0538e?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -31,7 +31,7 @@
   "homepage": "https://github.com/nodeshift/rhoaster",
   "devDependencies": {
     "coveralls": "^3.0.7",
-    "eslint": "^6.5.1",
+    "eslint": "^6.8.0",
     "eslint-config-semistandard": "^15.0.0",
     "eslint-config-standard": "^14.1.0",
     "eslint-plugin-import": "^2.17.3",