fix(package): update eslint to version 6.3.0

Closes #184

Author: greenkeeper[bot]

package.json

@@ -14,7 +14,7 @@
   "dependencies": {
     "babel-eslint": "^8.0.3",
     "enzyme-to-json": "^3.2.2",
-    "eslint": "^4.13.0",
+    "eslint": "^6.3.0",
     "expect": "^22.0.0",
     "firebase": "^4.8.0",
     "history": "^4.7.2",