Fixed Gradle setup

android/build.gradle

@@ -1,22 +1,31 @@
 buildscript {
-    repositories {
-        jcenter()
-    }
+    // 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 {
+            google()
+            jcenter()
+        }
 
-    dependencies {
-        classpath 'com.android.tools.build:gradle:1.3.1'
+        dependencies {
+            classpath("com.android.tools.build:gradle:3.6.3")
+        }
     }
 }
 
 apply plugin: 'com.android.library'
 
+def safeExtGet(prop, fallback) {
+    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+}
+
 android {
-    compileSdkVersion 27
-    buildToolsVersion '27.0.3'
+    compileSdkVersion safeExtGet('compileSdkVersion', 29)
 
     defaultConfig {
-        minSdkVersion 16
-        targetSdkVersion 27
+        minSdkVersion safeExtGet('minSdkVersion', 16)
+        targetSdkVersion safeExtGet('targetSdkVersion', 29)
         versionCode 1
         versionName "1.0"
     }
@@ -30,6 +39,8 @@ repositories {
     maven {
         url "$projectDir/../../react-native/android"
     }
+    google()
+    jcenter()
 }
 
 dependencies {