Bump eslint from 3.19.0 to 7.6.0

Bumps [eslint](https://github.com/eslint/eslint) from 3.19.0 to 7.6.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v3.19.0...v7.6.0)

Signed-off-by: dependabot[bot] <support@github.com>

.travis.yml

@@ -9,6 +9,7 @@ node_js:
 
 os:
   - linux
+  - osx
 
 services:
   - docker

package.json

@@ -29,7 +29,7 @@
         "babel-preset-es2015": "^6.24.1",
         "babel-preset-es2015-rollup": "^3.0.0",
         "chai": "^4.1.2",
-        "eslint": "^3.19.0",
+        "eslint": "^7.6.0",
         "mocha": "^3.5.3",
         "rollup": "^0.50.0",
         "rollup-plugin-babel": "^3.0.2",