Bump eslint

Bumps [eslint](https://github.com/eslint/eslint) from 3.19.0 to 6.8.0. - [Release notes](https://github.com/eslint/eslint/releases) - [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md) - [Commits](eslint/eslint@v3.19.0...v6.8.0) Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

conferences/rstudio_supervised_learning_dc_2019/Materials/Part_2_Basic_Principles_files/leaflet-providers-1.1.17/package.json

@@ -26,7 +26,7 @@
  ],
  "devDependencies": {
  "chai": "^4.1.2",
- "eslint": "^3.16.1",
+ "eslint": "^6.8.0",
  "eslint-plugin-html": "^2.0.1",
  "mocha": "^3.2.0",
  "mocha-phantomjs-core": "^2.1.1",