updating testing packages

package.json

@@ -86,8 +86,8 @@
     "winston": "^1.0.1"
   },
   "devDependencies": {
-    "chai": "^3.0.0",
-    "chai-as-promised": "^5.1.0",
+    "chai": "^4.2.0",
+    "chai-as-promised": "^7.1.1",
     "coveralls": "^3.0.1",
     "eslint": "^4.19.1",
     "eslint-plugin-prettier": "^2.6.0",
@@ -100,9 +100,8 @@
     "nock": "^9.3.3",
     "nyc": "^11.6.0",
     "prettier": "1.11.1",
-    "sinon": "^1.17.4",
-    "sinon-as-promised": "^4.0.0",
-    "sinon-chai": "^2.8.0"
+    "sinon": "^6.3.4",
+    "sinon-chai": "^3.2.0"
   },
   "optionalDependencies": {
     "@google-cloud/functions-emulator": "^1.0.0-beta.5"