Merge pull request #40 from hexojs/dependabot/npm_and_yarn/sinon-tw-7.1.1

Update sinon requirement from ^6.3.5 to ^7.1.1

Author: segayuu

package.json

@@ -52,7 +52,7 @@
     "mocha": "^5.2.0",
     "proxyquire": "^1.7.9",
     "rewire": "^4.0.1",
-    "sinon": "^6.3.5"
+    "sinon": "^7.1.1"
   },
   "engines": {
     "node": ">=6.9.0"