Upgrade projects

Now using
- gradle wrapper v6.0
- androidx
- stable android gradle plugin v3.5.0
- target and compile sdk set to 29

using_firebase_db/android/app/build.gradle

@@ -25,7 +25,7 @@ apply plugin: 'com.android.application'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion 29
 
     lintOptions {
         disable 'InvalidPackage'
@@ -35,7 +35,7 @@ android {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "github.nisrulz.using_firebase_db"
         minSdkVersion 16
-        targetSdkVersion 28
+        targetSdkVersion 29
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

using_firebase_db/android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.2-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0-all.zip