Update dependency geckodriver to v1.18.0 (#506)

Author: renovate[bot]

package-lock.json

@@ -45,7 +45,7 @@
     "eslint": "6.4.0",
     "eslint-config-airbnb": "18.0.1",
     "eslint-plugin-import": "2.18.2",
-    "geckodriver": "1.17.0",
+    "geckodriver": "1.18.0",
     "istanbul": "0.4.5",
     "mkdirp": "0.5.1",
     "mocha": "6.2.0",