fix(@octokit/rest): update to version 15.4.0 (#40)

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
   },
   "contributors": [],
   "dependencies": {
-    "@octokit/rest": "15.2.7",
+    "@octokit/rest": "15.4.0",
     "bunyan": "1.8.12",
     "bunyan-format": "0.2.1",
     "dotenv": "5.0.1",