chore(package): update eslint to version 5.15.1

Closes #119

Author: greenkeeper[bot]

Diff for: package.json

@@ -99,7 +99,7 @@
     "babel-preset-flow": "^6.23.0",
     "codecov": "^3.0.0",
     "coveralls": "^3.0.0",
-    "eslint": "^4.7.2",
+    "eslint": "^5.15.1",
     "eslint-config-xo-space": "^0.17.0",
     "eslint-plugin-flowtype": "^2.36.0",
     "express": "^4.16.0",