Update build.gradle (#878)

Author: alexhernandez

android/build.gradle

@@ -20,6 +20,11 @@ buildscript {
 apply plugin: 'com.android.library'
 
 android {
+    def agpVersion = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION
+    if (agpVersion.tokenize('.')[0].toInteger() >= 7) {
+      namespace "com.rnappauth"
+    }
+
     compileSdkVersion safeExtGet('compileSdkVersion', 28)
     defaultConfig {
         minSdkVersion safeExtGet('minSdkVersion', 16)