fix: pin eslint to 5.15.3

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "chai": "^4.1.2",
     "chokidar-cli": "^1.2.0",
     "coveralls": "^3.0.1",
-    "eslint": "^5.0.0",
+    "eslint": "5.15.3",
     "eslint-config-toboid": "^2.0.0",
     "lodash": "^4.17.1",
     "mocha": "^6.0.0",