Update dependency webdriver-image-comparison to ^0.20.0

Author: renovate-bot

modules/nightwatch-image-comparison/package.json

@@ -9,7 +9,7 @@
     "access": "public"
   },
   "dependencies": {
-    "webdriver-image-comparison": "^0.18.0"
+    "webdriver-image-comparison": "^0.20.0"
   },
   "optionalDependencies": {
     "mocha": "^6",