chore(admob): update to minSdk 21

Author: thatfiredev

admob/app/build.gradle.kts

@@ -16,7 +16,7 @@ android {
 
  defaultConfig {
  applicationId = "com.google.samples.quickstart.admobexample"
- minSdk = 19
+ minSdk = 21
  targetSdk = 34
  versionCode = 1
  versionName = "1.0"