Upgrade projects

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

persist_key_value/android/app/build.gradle

@@ -16,7 +16,7 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 27
+    compileSdkVersion 29
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'
@@ -30,10 +30,10 @@ android {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "github.nisrulz.persistkeyvalue"
         minSdkVersion 16
-        targetSdkVersion 27
+        targetSdkVersion 29
         versionCode 1
         versionName "1.0"
-        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
 
     buildTypes {
@@ -52,6 +52,6 @@ flutter {
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
     testImplementation 'junit:junit:4.12'
-    androidTestImplementation 'com.android.support.test:runner:1.0.1'
-    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
+    androidTestImplementation 'androidx.test:runner:1.2.0'
+    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
 }