Update dependency eslint to v6 (#6)

* Update dependency eslint to v6

* Still allow eslint 5 usage

Co-authored-by: Renovate Bot <renovatebot@gmail.com>
Co-authored-by: Ryan Zimmerman <17342435+RyanZim@users.noreply.github.com>

package.json

@@ -29,12 +29,12 @@
   },
   "devDependencies": {
     "doctoc": "^1.3.0",
-    "eslint": "^5.0.0",
+    "eslint": "^6.0.0",
     "lodash.defaultsdeep": "^4.6.0",
     "prettier": "^1.5.2"
   },
   "peerDependencies": {
-    "eslint": "^5.0.0"
+    "eslint": "^6.0.0 || ^5.0.0"
   },
   "prettier": {
     "singleQuote": true,