chore(package): update eslint to version 6.7.1

Closes #11

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
   "devDependencies": {
     "babel-preset-es2015": "^6.3.13",
     "chai": "^3.4.1",
-    "eslint": "^3.10.2",
+    "eslint": "^6.7.1",
     "gulp": "^3.9.0",
     "gulp-babel": "^6.1.1",
     "gulp-eslint": "^3.0.1",