downgrade eslint, since it is broken in node 6

Author: nateps

package.json

@@ -21,7 +21,7 @@
   },
   "devDependencies": {
     "coveralls": "^3.0.5",
-    "eslint": "^6.0.1",
+    "eslint": "^5.16.0",
     "eslint-config-google": "^0.13.0",
     "expect.js": "^0.3.1",
     "mocha": "^6.1.4",