chore(package): update semantic-release to version 15.1.2

Closes #32

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "jest": "^21.0.0",
     "lint-staged": "^4.0.0",
     "prettier": "^1.0.0",
-    "semantic-release": "^7.0.1"
+    "semantic-release": "^15.1.2"
   },
   "files": [
     "umd.js"