chore(deps): update dependency mocha to v6 (#330)

Author: renovate[bot]

package.json

@@ -59,7 +59,7 @@
  "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": "^1.13.6",

samples/package.json

@@ -25,7 +25,7 @@
  "@google-cloud/storage": "^2.0.0",
  "chai": "^4.2.0",
  "execa": "^1.0.0",
- "mocha": "^5.0.0",
+ "mocha": "^6.0.0",
  "uuid": "^3.2.1"
  }
 }