chore(dependencies): update eslint

Keep the eslint version fresh, so we don't fall too far behind and have
trouble updating later.

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

Author: miketheman

package.json

@@ -44,7 +44,7 @@
     "format": "prettier --write index.js lib/*.js test.js"
   },
   "devDependencies": {
-    "eslint": "^5.16.0",
+    "eslint": "^6.8.0",
     "prettier": "*",
     "cross-spawn": "*",
     "deasync-promise": "*",