chore(package): Update sinon to the latest version 🚀 (#104)

Author: greenkeeper[bot]

handwritten/datastore/.circleci/config.yml

@@ -129,6 +129,7 @@ jobs:
             cd samples/
             npm link @google-cloud/datastore
             npm install
+            npm link @google-cloud/datastore
             cd ..
           environment:
             NPM_CONFIG_PREFIX: /home/node/.npm-global

handwritten/datastore/package.json

@@ -97,6 +97,6 @@
     "power-assert": "^1.5.0",
     "prettier": "^1.13.5",
     "proxyquire": "^2.0.1",
-    "sinon": "^5.1.1"
+    "sinon": "^6.0.0"
   }
 }