chore(deps): update dependency mocha to v6 (#305)

Author: renovate[bot]

packages/google-cloud-node/package.json

@@ -60,7 +60,7 @@
     "jsdoc-baseline": "git+https://github.com/hegemonic/jsdoc-baseline.git",
     "intelli-espower-loader": "^1.0.1",
     "jsdoc": "^3.5.5",
-    "mocha": "^5.2.0",
+    "mocha": "^6.0.0",
     "nyc": "^13.0.0",
     "power-assert": "^1.6.0",
     "prettier": "^1.13.5",

packages/google-cloud-node/samples/package.json

@@ -19,7 +19,7 @@
   "devDependencies": {
     "chai": "^4.2.0",
     "execa": "^1.0.0",
-    "mocha": "^5.2.0",
+    "mocha": "^6.0.0",
     "uuid": "^3.3.0"
   }
 }