chore(package): update eslint to version 6.3.0

Closes #12

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
   "homepage": "https://github.com/Intellicode/graphql-resolver-cache#readme",
   "devDependencies": {
     "coveralls": "^3.0.0",
-    "eslint": "^4.4.1",
+    "eslint": "^6.3.0",
     "eslint-config-prettier": "^2.3.0",
     "husky": "^0.14.3",
     "jest": "^21.0.0",