chore(package): update sinon to version 2.0.0-pre.6 (#19)

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -42,11 +42,11 @@
     "simple-bufferstream": "~1.0.0"
   },
   "devDependencies": {
-    "chai": "~3.5.0",
-    "express": "~4.14.0",
-    "mocha": "~3.3.0",
-    "sinon": "~1.17.4",
-    "sinon-chai": "~2.9.0",
-    "supertest": "~2.0.1"
+    "chai": "^3.5.0",
+    "express": "^4.14.0",
+    "mocha": "^3.3.0",
+    "sinon": "^2.1.0",
+    "sinon-chai": "^2.9.0",
+    "supertest": "^2.0.1"
   }
 }