chore(package): update semantic-release to version 15.0.0

Closes #17

Author: greenkeeper[bot]

package.json

@@ -51,7 +51,7 @@
     "mocha": "3.4.2",
     "mocha-sinon": "2.0.0",
     "nyc": "11.0.3",
-    "semantic-release": "6.3.6",
+    "semantic-release": "15.0.0",
     "sinon": "2.3.6",
     "sinon-chai": "2.11.0",
     "validate-commit-msg": "2.12.3"