Updated to work with newer versions of RN (#247)

* Updated to work with newer versions of RN

* Revert back to compile as it could break projects using RN < 0.57

* Fix buildToolsVersion

Author: mrkpatchaa

android/build.gradle

@@ -1,23 +1,30 @@
+def safeExtGet(prop, fallback) {
+    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+}
 
 buildscript {
     repositories {
+        maven {
+            url 'https://maven.google.com/'
+            name 'Google'
+        }
         jcenter()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.2'
+        classpath 'com.android.tools.build:gradle:3.2.1'
     }
 }
 
 apply plugin: 'com.android.library'
 
 android {
-    compileSdkVersion 27
-    buildToolsVersion '28.0.2'
+    compileSdkVersion safeExtGet('compileSdkVersion', 27)
+    buildToolsVersion safeExtGet('buildToolsVersion', '28.0.2')
 
     defaultConfig {
-        minSdkVersion 16
-        targetSdkVersion 26
+        minSdkVersion safeExtGet('minSdkVersion', 16)
+        targetSdkVersion safeExtGet('targetSdkVersion', 26)
         versionCode 1
         versionName "1.0"
         manifestPlaceholders = [
@@ -34,6 +41,6 @@ repositories {
 }
 
 dependencies {
-    compile 'com.facebook.react:react-native:+'
-    compile "net.openid:appauth:0.7.1"
+    compile 'com.facebook.react:react-native:'+safeExtGet('reactNativeVersion', '+')
+    compile 'net.openid:appauth:0.7.1'
 }