Upgrade gradle setup

android/build.gradle

@@ -1,10 +1,16 @@
 buildscript {
-    repositories {
-        jcenter()
-    }
-
-    dependencies {
-        classpath 'com.android.tools.build:gradle:1.3.1'
+	// The Android Gradle plugin is only required when opening the android folder stand-alone.
+    // This avoids unnecessary downloads and potential conflicts when the library is included as a
+    // module dependency in an application project.
+    if (project == rootProject) {
+        repositories {
+            mavenCentral()
+	    google()
+        }
+
+        dependencies {
+            classpath("com.android.tools.build:gradle:3.5.3")
+        }
     }
 }
 
@@ -15,12 +21,12 @@ def safeExtGet(prop, fallback) {
 }
 
 android {
-    compileSdkVersion safeExtGet('compileSdkVersion', '23')
-    buildToolsVersion safeExtGet('buildToolsVersion', '23.0.1')
+    compileSdkVersion safeExtGet('compileSdkVersion', '28')
+    buildToolsVersion safeExtGet('buildToolsVersion', '28.0.3')
 
     defaultConfig {
         minSdkVersion safeExtGet('minSdkVersion', '16')
-        targetSdkVersion safeExtGet('targetSdkVersion', '22')
+        targetSdkVersion safeExtGet('targetSdkVersion', '28')
         versionCode 1
         versionName "1.0"
     }
@@ -31,6 +37,7 @@ android {
 
 repositories {
     mavenCentral()
+    google()
 }
 
 dependencies {

android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,5 @@
-#Wed Apr 10 15:27:10 PDT 2013
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.2.1-all.zip