Update firestore version as per launch cal (#202)
Update firestore version as per launch cal (#202)

* bump firestore version so that we can release the right version

* update to 18 as per the launchcal

firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk