chore(package): update semantic-release to version 15.1.4

Closes #17

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "lint-staged": "^7.0.0",
     "prettier": "^1.9.2",
     "projectz": "^1.4.0",
-    "semantic-release": "^12.2.2",
+    "semantic-release": "^15.1.4",
     "travis-deploy-once": "^4.3.1"
   },
   "scripts": {