chore(package): update sinon to version 8.1.0

Closes #17

Author: greenkeeper[bot]

package.json

@@ -59,7 +59,7 @@
     "rollup": "^0.60.0",
     "rollup-plugin-babel": "^3.0.3",
     "semantic-release": "^15.13.13",
-    "sinon": "^6.0.0",
+    "sinon": "^8.1.0",
     "sinon-stub-promise": "^4.0.0",
     "travis-deploy-once": "^5.0.0",
     "vue": "^2.5.13"