chore(package): update webdriverio to version 5.2.8

Closes #336

Author: greenkeeper[bot]

package.json

@@ -84,7 +84,7 @@
     "wdio-selenium-standalone-service": "0.0.10",
     "wdio-spec-reporter": "^0.1.2",
     "wdio-webpack-service": "^1.0.1",
-    "webdriverio": "^4.10.2",
+    "webdriverio": "^5.2.8",
     "webpack": "4.7.0",
     "webpack-cli": "^2.0.12",
     "webpack-dev-middleware": "3.1.3"