react-native-firebase

docs(admob): document serverSideVerificationOptions (#4096)

* Implemented Server Side Verification for AdMob

* added e2e test case for AdMob serverSideVerificationOptions

* Fixed eslint error on AdMob validateAdRequestOptions

* Added missing imports for AdMob Android

* Updated AdMob document for explaining how to use serverSideVerificationOptions.

* Update displaying-ads.md

* Update docs/admob/displaying-ads.md

* Update docs/admob/displaying-ads.md

* Update .spellcheck.dict.txt

Co-authored-by: Mike Diarmid <mike.diarmid@gmail.com>