Update dependency mocha to v6.2.0 (#479)

Author: renovate[bot]

package-lock.json

@@ -46,7 +46,7 @@
     "geckodriver": "1.16.2",
     "istanbul": "0.4.5",
     "mkdirp": "0.5.1",
-    "mocha": "6.1.4",
+    "mocha": "6.2.0",
     "portfinder": "1.0.21",
     "selenium-assistant": "5.4.0",
     "semver": "6.2.0",