chore(package): update semantic-release to version 15.13.31

Closes #13

Author: greenkeeper[bot]

package.json

@@ -13,7 +13,7 @@
   },
   "devDependencies": {
     "standard": "^8.0.0",
-    "semantic-release": "^6.3.2",
+    "semantic-release": "^15.13.31",
     "greenkeeper-postpublish": "^1.0.0"
   },
   "homepage": "https://greenkeeper.io",