Rolled back sinon version to support node 0.10 (travis requirements)

Author: tot-ra

package.json

@@ -37,6 +37,6 @@
     "chai": "^4.1.2",
     "mocha": "^3.2.0",
     "proxyquire": "^2.0.1",
-    "sinon": "^4.4.10"
+    "sinon": "^3.2.0"
   }
 }